Search Results

Riparian Woodlands 1999-01-01 Plant Communities of Mount Diablo State Park Excerpted from MDIA's book Plants of the East Bay Parks, by Glenn Keator, Ph. D. Madrone Canyon | Mike Woodring Riparian woodland is found only along permanent streams and rivers, where the water table remains at or just below the surface all year. Our area has no true rivers, but there are several perennial streams -- some with fairly broad floodplains -- that support riparian woodland. Because riparian woodlands have a guaranteed water supply, their component trees are very different from trees in most other environmental situations. These trees are not limited by the hot, dry days of summer; rather they can afford to grow fast and profligately right through the longest days of the year. Consequently, the derivation of riparian woodlands is entirely different from that of the rest of our flora. The closest relatives to riparian species come from summer-wet climates such as those across the Midwest and eastern parts of the United states. Wander in these forests if you are homesick for the look and feel of eastern hardwood forests. Riparian trees -- because of their ancestry from eastern United States climates -- behave as though they still were adapted to cold winters. Nearly all are deciduous in winter, for they can afford to make whole new sets of leaves the following year, come what may. Leaves are also designed in ways that suggest water wastefulness: they're broad, thin, often lobed or compound, and held horizontally -- fully exposed to the summer sun. They are also borne in thick tiers from top to bottom. Riparian trees reach maturity quickly because they're able to grow over such long periods each year. Quick growth may cause weak wood, however, and many riparian trees are liabilities because of brittle limbs. They also have relatively short life spans. BACK TO LIST

Alameda Whipsnake 1997-02-05 Placed on Federal Threatened Species List by Scott Hein On February 5, 1997, the Alameda Whipsnake was added to the federal government's list of threatened species. The action by the U.S. Fish and Wildlife Service means the snake is eligible for federal habitat protection and restoration funding. The whipsnake is sooty black with yellow-orange stripes running the length of its body. It can grow to 4 feet and is found most abundantly in Mount Diablo State Park. It eats lizards, rattlesnakes, small mammals and birds. The snake is known for its speed, which it generally uses to retreat from humans. BACK TO LIST

Mary Bowerman Trail 2014-05-01 Reproduced from Mountain News Spring/Summer 2014 by J. Frank Valle-Riestra Mike Woodring In 2024 we celebrated the 50th anniversary of the founding of the Mount Diablo Interpretive Association. One of the first major projects undertaken by the infant association was a survey of the park’s trails network. Small groups of dedicated hiker-environmentalists spread out over the far reaches of the park as it was in the mid-’70s, assessing the existing trails and recommending new trails. One recommendation was construction of what is now known as the Mary Bowerman Trail. The summit of the main peak was a primary destination of the visiting public, but no trails were there for visitors to experience close contact with the mountain’s exceptional natural environment. The first step was to lay out a possible route. Surveys of the topography revealed that a logical circuit of the summit region could be visualized with no anticipated damage to plant life and geological formations. The circuit was to be fairly level, along a contour line, with an overall distance of about a mile. Full of enthusiasm, our little band of interpreters marked the route with wooden stakes with red ribbons. We came back a few days later to find almost all of the stakes gone! So back we went and repeated our layout. A couple of days later, the same thing! And then it dawned on us. This was not the work of vandals, it was the work of animals (raccoons? skunks?) resenting this intrusion into their homeland. This was one of many delays; some, as expected, came as a result of environmental reviews by the Department of Parks and Recreation in Sacramento. Finally, with preliminary approval, Park Ranger Dick VanEtta single-handedly constructed a primitive path along the proposed circuit, in just a few days. But all in vain. For it was August of 1977, and soon after VanEtta’s efforts, lightning struck on Twin Peaks, and the resulting fire roared upward toward the summit. The summit buildings were saved, but the fire destroyed the plants on the north-facing slopes below, as well as vestiges of the new trail. The Bay Area was stunned by the damage to the park, and money poured in to help regeneration, along with suggestions which simply proved that many kind-hearted people did not understand that post-fire regeneration was best left to nature. Proposals such as aerial scattering of grass seeds, planting of redwood groves, even introducing palm trees were mercifully rejected. But the money was put to good use. The decision was made to build the trail as originally envisioned, through the burnt area, and to dedicate the trail to fire interpretation. After almost five years of planning, a spectacular trail, The Fire Interpretive Trail, was completed in 1982 by a wonderful group of young people from the California Conservation Corps, under the direction of Carlos Espinoza, a dynamo in a wheelchair. A grand trail dedication was held at the trailhead, with lots of visiting celebrities, fluttering flags, and politicians. William Penn Mott Jr., then superintendent of California State Parks, spoke, as did Senator John Nejedly and Mary Leo Bowerman, celebrated botanizer of Mount Diablo. Dr. Bowerman was a founding member of MDIA and co-founder of Save Mount Diablo, our sister organization. Dr. Bowerman passed away in 2005 at the age of 97; The Fire Interpretive Trail was renamed in her honor. Following extensive incineration during the recent Morgan Fire, the trail continues to serve as a fire interpretive trail, to allow the public to monitor post-fire recovery of the plant communities over the coming years. Ironically, Dr. Bowerman did not originally favor a trail through the area. She was afraid, with some justification, that the construction effort and large visitor volume would impact the fragile plant life. Fortunately, rare and sensitive plants such as Bitterroot (Lewisia Redidiva) have fared well. The trail has been developed as a nature trail, and numbered posts refer to some highlights listed in a brochure available in a box at the trailhead. The 0.7-mile loop is no great challenge to the dedicated hiker, but with the help of the trail brochure, it offers an unusual range of discoveries. There is actually much more to see than the described features at the numbered posts, and close observation rewards you with some surprises. For instance, upon reaching the wooden platform called “The Bridge”, you might notice in the lower right corner a textbook example of a geological nonconformity. This is a phenomenon of two different rock types (in this case, shale and greenstone) being joined together along a seam. This kind of sudden change implies that the two rock types, formed separately perhaps millions of years apart, were squeezed and rubbed together by displacement forces, such as the upward thrust of the mountain’s piercement structure. On the trail’s southern rocky section, look for evidence of “slickensides”, highly polished surfaces formed by friction between rock masses moving relative to one another. During the spring months, be on the lookout for some unusual wildflowers. Just beyond The Bridge, at the point where the trail turns sharply toward the east, you pass a cherty scree slope on your right. Close inspection of the loose rocks will reveal the presence of small plants struggling to come to the surface, in the shape of small green spiders about the size of a tarantula. These are examples of Bitterroot, and if you are lucky, you will be there to welcome the spectacular white blooms. Other flowers worthy of attention: Brewer’s Rock Cress, seemingly growing out of the rock, in greenstone crevices in the cliff behind The Bridge. Astounding fields of pink Claytonia smothering an expanse of broken chert just before you reach the short side trail to Devil’s Pulpit. The side trail is often graced in June with Mariposa Lilies, and miniature Penstemon fight to survive at the base of the Devil’s Pulpit monolith, a favorite climbing rock. Ah, there are so many wonderful things to see on this trail, which, along with MDIA, has now been with us some fifty years. After parking your car at the lower summit parking lot, walk up a few steps to the trailhead, at the bottom of the steep one-way road leading to the summit. A clockwise circuit is recommended; you will finish your hike just across the road from the trailhead. Enjoy and celebrate! Mary Bowerman Interpretive Trail Guide Check out more Spring Wildflower Hikes: Globe Lily Trail Springtime in North Peak Black Point Trail Mary Bowerman Trail Map by Kevin Hintsa Mary Bowerman Trail Fire Recovery BACK TO LIST

Clayton Quarry 2004-04-01 Article furnished courtesy of RMC Pacific Materials By George Allen, Plant Manager Mount Diablo Review, Spring 2004 Clayton Quarry Two partners, Harrison and Birdwell, developed mining for construction aggregates on Mount Zion in 1947. However, this was not the first mining activity to occur in the area. The discovery of coal in approximately the 1850's brought about the first commercial mining and the subsequent settlement of coal mining towns such as Stewartville, Somersville, and Nortonville. The discovery of coal also led to additional prospecting wherein mercury and copper were discovered. It has been written that a "copper rush" occurred in the 1860's around Mount Diablo. Copper was never found in significant quantity to make commercial mining worthwhile but the Mt. Diablo mine did produce mercury until the 1950's. Gold and silver were also reported in various assays but, again, none was ever found in significant quantity to make commercial mining worthwhile. As a result of the search for the precious metals, mines and/or claims with names such as Great Republic, Superior, Pioneer, Horse Shoe, Rising Sun, San Carlos, Rough and Ready, and numerous others were developed. Today, the diggings of the Mount Zion Copper Company, Summit of Zion, San Pedro, and a few other mines can still be seen. In 1947, Harrison and Birdwell developed the Clayton quarry. The first excavation was behind the current shop building, but it was shortly moved to the east and south because of better rock on that side. In 1954, Harrison and Birdwell sold out to Pacific Coast Aggregates (later named Pacific Cement and Aggregates), who in turn sold out to Lonestar Industries in 1965. In 1988, Lonestar partnered with RMC of London, England. Today the quarry is owned by RMC Pacific Materials, a wholly owned company of RMC Ltd. of England. The quarry is located on Mount Zion and the material mined is diabase, a hard, durable rock used in the construction of roads, buildings, rail lines, dams, and levees. Over 25 different products are made to supply construction needs. The State of California has designated Mount Zion as a mineral reserve to be used to supply the construction needs of Contra Costa County. Of all the rock shipped out of the quarry, typically 72% of it goes to public sector projects. Some of the specific projects we have been involved in are B.A.R.T. (50% of all the rail ballast came from Clayton), Interstate 580 & Interstate 680 freeways, Highway 4, Highway 24, the new Giants Stadium, the Los Vaqueros Dam, Concord Naval Weapons Station, Delta levees, and many other projects. The Clayton Quarry has been in continuous production for over 50 years, and expects to be producing for many years to come. Interesting Facts: 1. Mount Zion was also known as "Pyramid Hill". 2. Elevation of Mount Zion is 1635 Feet. 3. Minerals found in the quarry are malachite, azurite, iron pyrite, magnetite and calcite. Mount Zion Reflection | Mitchell Canyon BACK TO LIST

Clark's Sphinx Moth 2025-03-20 Who thought a moth could look so cool! by Dan Sandri Dan Sandri Try to focus on that green blur in front of a blossom, perhaps a Blue Dicks flower (Dichelostemma capitatum ) or vetch (Genus Vicia ). Is it a hummingbird? Perhaps. But it may be a Clark’s Sphinx moth too! This time of the year (from March to June), they are flying about the oak woodland and surrounding grasslands from flower to flower, drinking flower nectar from a variety of flowers. It moves so quickly to another flower, uncurling its long proboscis to reach into flowers. They are not abundant, but I see them nearly every year. Clark’s Sphinx moths have a greenish forewing and an orange hindwing that has a black band along its base. Clark’s Sphinx range from Baja California north to British Columbia, and east to Idaho, Wyoming and Utah, and can be found in Oak woodland foothills. They lay eggs on Elegant Clarkia (Clarkia unguiculata ), the sole host plant that their caterpillars feed on. The eggs hatch in about 10 days, and once fully grown, the caterpillars pupate in burrows dug under rocks or other objects. They overwinter there and emerge the following Spring. I hope you see one! Clark's Sphinx Moth (Proserpinus clarkiae) BACK TO LIST

Deer Flat Hike 2024-12-01 Reprinted from the MDIA E-Newsletter December 2024 by Steve Smith Steve Smith As wet weather and winter sets in the question arises, where to hike with limited mud? One of the best options is to head up Mitchell Canyon Road to Deer Flat (and beyond). This hike is a 7.3 mile out-and-back with 1550 feet of climbing and features a fabulous surprise along the way. Starting at Mitchell Canyon, head up the canyon for a couple of miles. It is so lovely this time of year to have the constant melody of Mitchell Creek running alongside you. Watch for pops of color from Snowberry and Toyon, or even a myriad of fungi. But the true surprise awaits you 2 miles in as you will start to notice the bare twigs and trunks have taken on a unique coating...ladybugs! In their winter 'hybernation' are millions of convergent lady beetles in huge masses of color. Enjoy them here, and perhaps have a stop at the picnic tables, before you begin your ascent up the many switchbacks. Just before you start climbing you will see a volunteer trail off to your left heading to the creek. Take this lovely spur and have a quiet moment next to the old springbox dam just 50 yards up. This is a great place for a video with full sound of the rushing waters to share later. Now comes the climb! You will start up the crookedest road on Mount Diablo as you navigate 15 or so switchbacks. No matter how many times I hike this trail I'm always convinced that the next corner is the last corner...it never is. Take breaks along the way to gaze over at Eagle Peak looming above. In the latter part of December you should start seeing the urn-like blooms of Big Berry Manzanita. As you continue to climb you will be rewarded by either the views of the valley behind you, or the quiet solitude of a fog bank enveloping you. Once you finally do navigate that last corner, you will be greeted by a rest stop at Deer Flat with several tables to enjoy, and lovely views of Eagle Peak, Black Point and Mitchell Canyon. Take a moment. Your route back from here is simple, retrace your steps back the way you came and take notice of all the things you missed with a different perspective than on the way up. Of course if you want to extend your journey there are a multitude of ways back which incorporate a loop. Buyer beware, those other routes can be a bit tricky in the winter (Eagle Peak, Back Creek, Meridian Ridge). Ladybugs Switchbacks Map of Deer Flat Hike BACK TO LIST

Guide to Mount Diablo Geology 1998-07-01 Mount Diablo's Rocks, Tetonic History and Mining Wind Cave | Roi Peers Part I: The Rocks of Mount Diablo - Their Type and History Rising 3,849 feet, Mount Diablo forms a prominent feature in the East Bay landscape. Our understanding of the geological history of the rocks and structure of Mount Diablo has undergone major changes during the past 30 years, and even now geologists are still trying to unravel the complicated history of the mountain. This complex history is not unique to the mountain, but to our region as a whole, since Mount Diablo has been caught up in the processes that have shaped the Coast Ranges for millions of years. Perhaps the most salient fact is that, although the rocks of which it is composed are very old, Mount Diablo only began rising recently in geological terms. The rocks are old, but the mountain itself is young. To better understand the complex geology of Mount Diablo, it is useful to divide the mountain’s rocks into three main groups. Each group has a different history and is characterized by different types of rocks. Group 1: Mount Diablo Ophiolite ( Jurassic ) Group 2: Franciscan Complex ( Jurassic and Cretaceous ) Group 3: Great Valley Group ( Jurassic and Cretaceous ) and Younger Sedimentary rocks ( Cenozoic ) Plate tectonics played a major part in the formation of the Mesozoic rocks of Mount Diablo. We now recognize at least 11 separate major plates of oceanic crust and rigid upper mantle rocks around the globe. These plates “float” on a layer of semi-molten rock, all moving against and jostling each other, creating new land forms in the process. Continents ride atop these ocean plates, being rafted along as the plates move. New oceanic crust is being continually created by the eruption of submarine volcanic material forming along ocean-spreading ridges such as the Mid-Atlantic Ridge. To compensate for the newly created oceanic crust, older existing oceanic crust is driven beneath the continental crust at subduction zones, and recycled into the earth. Group 1 - Mount Diablo Ophiolite ( Jurassic-Cretaceous ) It is generally believed that near the close of the Jurassic a subduction zone developed along what is presently represented by the modern California coast. The oceanic crust caught between this subduction zone and an earlier shoreline in the ancient Sierra foothills was preserved as the Coast Range Ophiolite and later partially exposed. Ophiolites are thought to form at oceanic spreading centers in the middle of the oceans, associated with oceanic island chains (arcs), or in narrow oceans such as the Gulf of California. Ophiolites generally form a uniform vertical rock sequence consisting, from bottom to top, of ultramafic peridotite from the top of the mantle, mafic intrusive gabbros and/or diabase that formed one or more miles below the sea floor, and mafic extrusive rocks, often in the form of pillow lava extruded beneath water. The rocks of this old ocean crust on Mount Diablo have been named the Mount Diablo Ophiolite and is considered a fragment of the Coast Range Ophiolite. The Mount Diablo Ophiolite underlies the mountain north of a line drawn from Long Ridge through Murchio Gap, encompassing the Zion Peak rock quarry, Mitchell Rock, and Eagle Peak. Radiometric and fossil-age determinations date the ophiolite as having been formed approximately 165 million years ago during the Mid-Jurassic. Mount Diablo Ophiolite Basalt: The basalt, which makes up the upper part of the Mount Diablo Ophiolite, is mostly interbedded pillow basalt lava flows. As the lava erupts under water, the outer surface of the flow “freezes” in contact with the water. More lava breaks through and again the outer surface “freezes.” This process leads to the accumulation of “pillow” structures and the resultant rock is referred to as pillow basalt or pillow lava. The basalt has a microscopic crystalline texture with a black to greenish-brown color, weathering to a yellowish-brown to dark reddish-brown soil. Well-developed pillows can be seen on Mitchell Rock. Mount Diablo Diabase: The pillow lavas are fed by a series of vertical fissures, or dikes, that allow the molten rock from below to reach the surface. The molten material in the dikes solidifies into a rock called diabase, which has the same chemical composition as basalt, but with a coarser texture. Diabase is exposed in quarries at Mt. Zion and on Eagle Peak. Mount Diablo Serpentinite: Serpentinite is a rock frequently found in association with an ophiolite. Serpentinite is derived from the basal portion of the original ocean crust and uppermost part of the mantle, but has been metamorphosed by hydration from ocean water circulating through fractures in the ocean crust. Serpentinite forms by addition of water to minerals in peridotite, changing them from olivine and/or pyroxene to the serpentine minerals antigorite, chrysotile and lizardite. Serpentinite, incidentally, is California’s state rock. On Mount Diablo, serpentinite occurs in several localities. The largest is the prominent east-west band that runs through Murchio Gap extending west along Long Ridge, separating the ophiolite on the north from the Franciscan rocks exposed in the central core of the mountain to the south. This band is characterized by a noticeable change in vegetation due to the high magnesium content of the serpentinite. Exposures of the serpentinite are typically pale green to greenish-gray, locally black, weathering to grayish-orange. In addition to the highly sheared serpentinite, ultramafic rocks of harzburgite (a variety of peridotite) and pyroxenite are present in this band as well, but are less sheared than the serpentinite. The body of pyroxenite exposed along the Burma Road Trail on Long Ridge is coarsely crystalline, sparkling in the sunlight as you walk along the trail. Exposed blocks of massive harzburgite on the westerly end of Long Ridge frequently contain veins of fibrous chrysotile. There are several pods of silica carbonate rock (altered serpentinite) found in association with the mercury mines on the northeast flank of the mountain and other scattered locations along the serpentinite band. Group 2 - Franciscan Complex ( Mesozoic ) The central Mount Diablo summit area and North Peak is underlain by an assemblage of Mesozoic rocks that have been a puzzle to California geologists for years. Our relatively new understanding of plate tectonics and subduction has finally provided an important clue to unraveling this mystery. This diverse complex of rock types is common up and down the coastal ranges of California and has been given the name Franciscan Complex. The processes of subduction can account for the mixing of such a wide variety of rock materials. The Franciscan Complex records over 140 million years of uninterrupted east-dipping subduction, during which the Franciscan formed as an accretionary complex. As the oceanic plate subducted beneath the continent, part of the upper section of the ocean crust (pillow basalt) and the material riding on the plate (chert, graywacke, shale, small islands, and sea mounts) were scraped off the upper part of the subducting plate, mixed together, partially subducted and accreted on and under the continental crust. Mount Diablo and North Peak are composed of faulted blocks of resistant basalt and chert with some graywacke and minor shale, and are expressed topographically as rugged and jagged rock masses. Wrapping around the two peaks in a rough “figure 8” shape are the more gentle treeless slopes of “mélange.” Such a diverse mixture of rocks, is called a "mélange" by geologists from the French for "mixture". The Franciscan mélange is essentially a chaotic mixture of an intensely sheared sandstone and shale “paste” in which are embedded blocks of basalt, chert, and graywacke along with rare exotic rocks. It is often difficult to distinguish between the mélange topography and local landslides. Franciscan rock accretion ceased with the ending of subduction in our area. Franciscan-like rocks are currently forming north of Cape Mendocino offshore or beneath the continent where the oceanic Juan de Fuca plate is still subducting beneath North America. Recent studies using modern dating techniques and temperature history studies suggest that the Franciscan Complex appears to have undergone metamorphism around 108 million years ago at a depth of approximately 12 miles. As a result, the Franciscan rocks are frequently referred to as metabasalt or metagraywacke reflecting a history of metamorphism by heat and pressure deep underground. Franciscan basalt: The blocks of basalt exposed in the Franciscan on Mount Diablo are altered oceanic pillow basalt. On the surface the rock weathers to a dark yellowish-brown to dark reddish-brown while fresh exposures are grayish-green to light olive drab. It is locally called “greenstone.” The green color comes mostly from chlorite, a green alteration mineral. The basalt blocks in the Franciscan are believed to be fragments scraped off of the upper part of subducting basaltic oceanic crust. Franciscan chert: The chert bodies in the Franciscan form prominent dark red exposures and talus slopes. Made up of silica, they are resistant to erosion and form such features as Devil’s Pulpit and Turtle Rock. Typically red in color (green and white less common), the chert layers are typically interbedded with reddish-colored shale. These banded rocks are often referred to as “ribbon chert.” The red color is derived from iron oxides. The chert in the Franciscan was formed far out at sea. Silica skeletons of minute ocean animals called radiolaria settled to the ocean floor forming a silica ooze that ultimately solidified into chert. The chert continued to slowly accumulate on top of the ocean floor as the ocean crust drifted away from the spreading center on its long journey toward subduction. The Franciscan chert ranges in age from 190 myo (million years old) to 90 myo, representing 100 million years of accumulation. Franciscan cherts are formed from the tiny (0.5 to 1.5 mm) silica shells of radiolaria. Many of these radiolaria are tropical species indicating that the sediments were deposited near the equator and were later transported northeastward by plate movements. Franciscan graywacke: Graywacke is less common on Mount Diablo than the greenstone and chert. It is typically fine-to medium-grained and massive (no stratification or bedding visible). It breaks along distinct joint planes, which helps distinguish it in outcrop from the more “shatter fracturing” of the greenstone. The graywacke consists mainly of angular quartz, plagioclase feldspar, chert fragments, and dark volcanic rock fragments. Calcite and quartz occur commonly in the criss-crossed white veins. The graywacke is younger in age than the greenstone (basalt) or chert, ranging from 90 to 108 million years in age. These rocks are thought to have formed in a subduction trench environment off the coast of North America (some researchers suggest Mexico, subsequently moving north). Franciscan shale: Approximately 10% of the Franciscan on Mount Diablo is made up of shale, most of which has been altered to argillite as a result of the earlier period of metamorphism. Most of this clay-sized material was probably deposited in less turbulent current conditions in association with the graywacke deposition. Franciscan exotic rocks: The most common so-called exotic rock present on Mount Diablo is a glaucophane schist, or “blueschist,” named for the noticeable blue color of the glaucophane. Blue schist is largely altered basalt and reflects a history of hi-pressure/low-temperature metamorphism, a condition found in subduction environments and rarely any other place. On the Summit Road as you drive toward the summit, just past the Rocky Point Picnic area, you will notice a dark blue-black boulder of blueschist about five feet across protruding from the bank on the left side of the road. Group 3 - Great Valley ( Jurassic - Cretaceous ) and Younger Sedimentary Rocks ( Cenozoic ) The name Great Valley Group refers to the thick sedimentary rocks of Upper Jurassic through Cretaceous age that were deposited between the ancestral Sierra Nevada to the east and the subduction zone to the west on top of the ophiolite basement that underlies California’s central valley. The Great Valley sequence is composed mostly of deepwater marine shale, sandstone and some conglomerates accumulating to a thickness of 60,000 feet near the western margin of the present day Great Valley, and then, in our area, thinning toward Mt. Diablo. The Upper Jurassic Knoxville Formation is 140 million years old and are the oldest beds of Great Valley in this area. Great Valley deposits on-lap the Mount Diablo area and thinner deposits intermittently covered it during this time. The general interpretation of these rocks is that they were deposited in the submerged central valley as intermittent underwater "turbidity currents" and the deposits are called turbidites. To summarize the Cenozoic in this area, it is perhaps easiest to think of the central valley of California as a low elongate basin, flooded intermittently by an encroaching shallow sea, and slowly being filled by sedimentary material eroded from the surrounding exposed land masses, primarily the “Sierra.” During the latter part of the Tertiary, newly formed highlands to the south (Diablo Range) and in the area of the present day San Francisco Bay also acted as source areas. The Mount Diablo area seemed to represent a persistent “high,” underwater, but less deep than surrounding areas and periodically exposed to erosion. Many of the formations seem to shoal out on the flanks of this area and when submerged, the strata thin over this “high.” The area, however, was not a “mountain” as we see it today, but rather a land of low relief intermittently submerged well into the Pliocene. Paleocene Rocks (55.5 - 65 million years ago) There are few Paleocene deposits present in our area indicating that the region was probably above sea-level and undergoing erosion following the close of the Cretaceous. The only nearby rocks of this age are restricted to the north side of the mountain outside of the park. Eocene Rocks (33.7 - 55.5 million years ago) During the Eocene , the climate warmed, resulting in heavy “ancestral Sierra” weathering that yielded large quantities of sands that washed into and across the Central Valley providing material to the Eocene deposits of Mount Diablo. A shallow marine basin, a sandy shoreline, a swampy backwater area—all existed in this area at different times or at the same time in different places. On the north side of the mountain, the Eocene is present in the Black Diamond Mines Regional Park. These strata contain coal beds and glass sands and have been described as a near-shore lagoonal swamp or tidal flat estuarine environment. On Mount Diablo, Eocene deposits form the ridges of tan-colored sandy rock formations that wrap around the south and west side of the mountain. These sedimentary rocks have been given the name Domengine Formation and are well exposed at Castle Rock, Rock City, Knobcone Point, and Cave Point. These sands on the south side of the mountain are characteristic of deep offshore slope deposits. They represent deep erosion of the ancestral Sierra highland spreading over the Mount Diablo area as the ocean deepened westward. Some Domengine beds represent shallower near-shore deposits that contain beds rich in Turritella fossils (marine snails). These massive sandstone beds weather easily forming features such as caves and open tunnels. Rock City, easily accessible on the South Gate Road, is a good place to view these unusual features. These massive sandstone that form the Wind Cave beds weather easily forming features such as wind caves and open tunnels. Unusual "cannonball concretions" can also be found in these sandstone beds. Rock City is a good place to view these unusual features easily accessible on South Gate Road. Oligocene Rocks (23.8 - 33.7 million years ago) The only Oligocene rocks in the area is the Kirker Tuff on the north side of the mountain outside the park boundary. Miocene Rocks (23.7 - 5.3 million years ago) On the south and west sides of the mountain, the depositional contact between the Eoceneand the Miocene rocks can be recognized by the abrupt change from clean, thick-bedded, light tan sandstone in the Domengine formation (Eocene) to poorly sorted, dark gray, pebbly sandstone of the marine Miocene rocks. There is a large gap in the geologic time record between these rock units, representing erosion or non-deposition. The interval of missing time and rock equivalents includes the upper Eocene, the entire Oligocene and the lower (or earliest) Miocene. During middle Miocene time, the general drainage was directed from the east into an open ocean to the west, a pattern similar to the deposition of the earlier Eocene. By about 10 mya (million years ago), subduction had ended in central California and there was a major change in the pattern of deposition. A highland developed to the west and the Diablo Range south of Livermore began to rise. The Mount Diablo area began to accumulate marine and later non-marine deposits from these sources. Now steeply tilted upward from an original horizontal orientation, the vertical beds form the prominent “hogbacks” on Fossil Ridge and Blackhawk Ridge. Building material quarried from Fossil Ridge was used to construct the summit museum building, and numerous clam and oyster shells can be seen in the exterior walls of that building. These fossiliferous beds are called the Briones Formation. Following Briones deposition, the direction of sediment transport shifted again, bringing sands derived from the east, rich in volcanic material washed from the Sierra highlands. These volcanic sands have been named the Neroly formation. They form the grass-covered rounded hills immediately south of the underlying ridge-forming Briones strata on the south, and can be found on the west and north sides of the mountain as well. Andesitic Neroly sandstone alters easily, and in most places the sand grains are coated with a thin layer of bluish clay that is clearly exposed in an often visited site in Shell Ridge Open Space in Walnut Creek. Beds rich in fossil marine shells are well exposed at this site and also in Sycamore Canyon on the southern flank of Mt. Diablo. Around nine million years ago, during the late Miocene, the sea again receded from the Mount Diablo area, marking a permanent change from marine deposition to non-marine stream and lake deposition. One of the nine million-year-old stream deposits on the south side of the mountain has captured and preserved an abundant and diverse collection of animal fossils. The Blackhawk Ranch Quarry has yielded numerous vertebrate fossils of horses, rhinos, camels, and smaller animals. A large mastodon skull, a Gomphotherium , has been removed from this site. All give evidence that late Miocene mammals abounded in the newly created forests and flood plains stretching away to low hills to the west and south. There are several volcanic tuff deposits in the late Miocene and Pliocene derived from the volcanic fields of Sonoma County. There was still no Mount Diablo at the time. Plio-Pleistocene to recent rocks (5.3 million years ago to present) Non-marine deposits continued to collect in the area during Pliocene time (5.3-1.8). It was during Plio-Pleistocene time, by 4 mya and continuing to the present, that Mount Diablo was formed as a topographic feature. From that time on, Mount Diablo has been feeding erosion materials into surrounding valleys. Pliocene sources were predominantly from Great Valley rocks. Pleistocene sources were predominantly from Franciscan, indicating unroofing and erosion of deeper terranes. The 4.83 million-year-old Lawlor Tuff is a widespread marker bed around the mountain. The fact that it was laid down on a relatively flat landscape and is now steeply folded indicates that Mt. Diablo must have begun its growth after the tuff was deposited. Part II: Forming the Foundation - Mount Diablo's Tectonic History Although Mount Diablo is old in terms of its rock history, it is very young as a topographic feature. The rising of Mount Diablo to its present height is the result of a complex interplay of tectonic forces. The Franciscan Complex presumably underlies all of Contra Costa County. It was emplaced below the Coast Range Ophiolite by accretionary faulting during Cretaceous time, so the contact between the Franciscan and Coast Range Ophiolite (locally called the Mount Diablo Ophiolite) as well as the overlying Great Valley Sequence is everywhere a fault plane. This fault is known as the Coast Range fault. Recent field studies suggest that following the emplacement of the Franciscan Complex at depth in this area, the rocks underwent a period of metamorphism. This appears to have occurred at depths of approximately 12 miles. During late Cretaceous through early Eocene time, the overlying cover rocks were significantly thinned by extensional faulting along the Coast Range Fault plane and ductile thinning in the serpentinite component of the ophiolite. As a result of this slow structural thinning of the overburden, the Franciscan rocks of the future mountain rose vertically to a depth of around two miles. There appears to be no evidence that these rocks were above sea level during this period. The final two miles of uplift and exhumation of the Franciscan Rocks occurred during Pliocene to present time. It was during this last phase that the Franciscan rocks, and overlying Great Valley strata, were folded by compressional forces associated with what is believed to be a blind thrust fault beneath the mountain. These geological processes have created a complex uplifted compressional asymmetric fold that has been moving southwest on the blind thrust. The recognition of the possible existence of a blind thrust fault under Mount Diablo has resulted in the issuance of an advisory by the USGS in September, 1999, predicting a four-percent probability of a 6.7 or larger earthquake occurring on the blind thrust fault underlying the mountain. Geologists believe the mountain is still rising at about 2 millimeters per year. Extensive erosion has exposed the Franciscan in the center of the fold to produce the majestic Mount Diablo we see today. Part III: Mount Diablo Mining History - Boom to bust The most important minerals and rocks that have been mined or excavated on and around Mount Diablo include mercury, diabase, graywacke, white sands, coal, blue schists, travertine, copper, and farther north and east, gas and oil. Mercury Mercury has been mined on the northeast flank of Mount Diablo off and on since its discovery in 1863. Prior to that, Indians used the colored mineral for ceremonial purposes. The mercury (also referred to as quicksilver) occurs in the form of cinnabar (red mercury sulfide) and metacinnabar (a black mercury sulfide). The host rock for ore is silica-carbonate rock, itself formed from the hydrothermal alteration of serpentine, lying in the boundary fault zone that separates Franciscan from Great Valley rocks. The silica-carbonate rock is made up of varying quantities of silica (chalcedony and opal) together with magnesian carbonates and stained rusty red by alteration of iron sulfide minerals. The rock is commonly spongy in appearance. Topographically, silica-carbonate rock forms resistant outcrops. It is believed that the mercury minerals were deposited from hydrothermal solutions which formed mostly in fractures in the silica-carbonate rock. Ryne Mine produced most of the cinnabar while metacinnabar was produced at the Mount Diablo Mine. A man named Welch discovered cinnabar at what is known as the Ryne Mine in 1863. It operated for about 10 years before becoming uneconomic. In 1933 it was discovered that black metacinnabar in the area known as the Mount Diablo Mine also contained mercury and was more abundant than cinnabar. The demand for mercury during the second world war resulted in an expansion of operation that was to continue until 1958 when mining operations again ceased. It is estimated that about $1,500,000 worth of mercury was extracted from the mines. Unfortunately a continuing legacy of the mining is the acid mine water emptying into and contaminating Marsh Creek. Building Stones and Rip-rap The diabase quarries on the northside of the mountain (Zion Peak) are currently being excavated for crushed rock and rip rap material. There were several excavations in graywacke on the northside of the mountain for the same purposes, but they are now abandoned. Blue schist from the Franciscan rocks on Mount Diablo yielded good dimension stone and was popular for building construction due to its color. Copper and Precious Metals About 40,000 pounds of copper was produced from the mines in the diabase in the 1860's, but there is no activity now. Minor amounts of gold and silver associated with the copper were also produced. It was rumored that the best area to discover gold or silver was in the Back Canyon area (unfortunately inside the park boundary). Travertine Travertine, a finely crystalline massive calcium carbonate deposit frequently associated with hot springs, was quarried along the northside of Mount Diablo (Lime Ridge) for many years by the Cowell Cement Company. Coal and White Sand North of Mount Diablo and outside the park in the Black Diamond Mines area, lignite coal beds in the Domengine Formation were the largest known and most extensively mined Coal deposits in California. From the 1860's to the beginning of this century, the Mount Diablo coal field supplied coal to the rapidly expanding urban and industrial centers of the San Francisco Bay area. Finally closed as newer and cheaper energy sources were discovered, during its lifetime the mines produced approximately 4,000,000 tons of coal valued between $15 and $20 million. At the base of the Domengine Formation exposed in the Black Diamond Mines Regional Park, there is a thin section of white sands called the "Ione" sands, a description carried across the Central Valley from major white sand deposits in the Ione Formation on the east side of the Valley. The sands appear to be continuous across the valley subsurface and of equivalent age. The white sands, that were used for making glass, were mined from two deposits in the area from 1920 until 1949 when they ceased operation. The caverns are a fascinating place to visit on guided tours. Gas and Oil The Domengine Formation also acts as a reservoir for natural gas and the Martinez Formation produces oil in the subsurface northeast of Mount Diablo. Resource: Geologic Guide to Mount Diablo State Park Full color folding geology map of Mount Diablo State Park. Map side contains an overlay of our trail map showing the geologic formations that make up the mountain. The reverse contains detailed descriptions of formations, geologic timelines and more. A must have for all those interested in geology. Highly sheared serpentine | Roi Peers Franciscan graywacke sandstone | Roi Peers Franciscan beds of folded red chert | Roi Peers Turritella Fossils | Mike Woodring Wind Caves | Roi Peers BACK TO LIST

Tassajara Creek Hike 2024-06-01 Reprinted from the MDIA E-Newsletter June 2024 by Steve Smith Stephen Smith In the dog days of summer, it can sometimes be challenging to find a suitable hike on Mount Diablo. Tassajara Creek trail is a little out-of-the-way for most, off the beaten path, but partially shaded. Please note that the first and last ½ mile of this hike is along paved Finley Road until the new trailhead is built further up. Some consolation is offered in the pastures of horses, goats, geese, ponies and a llama along the way as well as the historic one-room Tassajara Schoolhouse on the drive there. This remote area of the park has many wonderful features including grand vistas of the Tassajara and Livermore Valleys as well as Cave Rocks and Cave Point. Rolling hills lead to a sheltered canyon at the headwaters of Tassajara Creek. Park on the shoulder of Finley Road and continue on foot for ½ mile to the entrance. You will first hike into EBRPD’s Morgan Territory up Old Finley Road. A left on Riggs Canyon Road will take you into MDSP. Continue for ¾ mile, Riggs Canyon will make a sharp left and begin climbing. At this bend look for an unsigned trail off to the right which will lead you 25 yards to Tassajara Creek. Turn left as you wind along the creek in the shaded canyon for 1 mile. Once you break out into the sunlight again, stop at the picnic table overlooking Bob’s Pond. Continue around the trail loop, now in full sun, as you wind along the base of Windy Point and Highland Ridge. At trail’s end, turn right on Highland Ridge Road, at the fork, stay right back onto Old Finley Road. Take this trail all the way back to the trailhead. Their are numerous side trips you can take including the Amphitheater Trail loop. This adventure takes you 8 miles with 1100 feet of climbing and is guaranteed to offer privacy, particularly on weekdays. Come early (or late) on weekends for parking. For directions to Finley Road trailhead, click here . For a route map click here . If you would like a .gpx file to help you navigate please download it here . Morgan Territory Tassajara Creek BACK TO LIST

Donner Canyon Hike 2023-09-01 A Fall hiking favorite! by Steve Smith Steve Smith As Fall descends upon us and cooler temperatures begin to prevail many of us return to regularly hiking the mountain. This is a time for fall foliage (namely Poison Oak), fall and winter berries, occasional rains and of course our beloved Tarantulas. This month's hike takes us on a tour of Donner Canyon (and some Mitchell and Back Canyons) where all these sights and more await you. This hike is 6-miles and 1,150 feet of climbing. Starting at Mitchell Canyon, head up the canyon to your first left on Oak Road. This is your first steep climb, but it is brief, and the views of the mountain await you. Continue straight onto the single-track Coulter Pine trail. Notice the namesake pine trees off to your right. (Note the needles on the Coulter and how they differ from the Ghost Pine—while the ghost has droopy relaxed needles, the Coulter's are erect like a toilet brush.) Continue to a right on Bruce Lee Road and cross Back Creek to a right on Back Creek Trail. At the first intersection, turn left up Tickwood Trail. Notice one of our largest stands of Poison Oak in its fall glory off to your right. Continue winding up and down the beautiful single-track through woodlands, grasslands, and chaparral until you reach the terminus at Donner Canyon Road. Turn right and then left about 200 yards up onto Donner Trail. Here you will have a lovely descent to Donner Creek through thick chaparral…this is a good place to see Tarantulas in the early morning or late afternoon. Turn left and follow the creek on Hetherington Trail. Just before the creek crossing, turn right and climb Bruce Lee Spring Trail. As you ascend the woodlands, be sure to turn around for a beautiful view of the Summit and North Peak. As the trail starts to level out, bear left at the intersection to remain on Bruce Lee Springs, winding through a dense stand of aromatic chaparral. At trail’s end, turn left on Clayton Oaks Road. You’ll spend the next mile and a half winding up and down through the grasslands where you are likely to spot deer and maybe a snake or two. As you approach Donner Canyon, you’ll make a right then a quick left onto Murchio Road. At the intersection at the top of the hill turn right onto Bruce Lee Road. Notice this area’s recovery following last May’s controlled burn. Continue down around Coulter Pond and watch for wildlife until you continue to the end and turn left on Watertower Road. Make a quick right on Bruce Lee Trail and head down the single track. Just to the left of the big iron gate is a lovely single track, Terrace Trail which will bring you back amongst the Oaks and offer views of the Mitchell Canyon entrance and Native Plant Garden before you make a pair of right turns to return on Mitchell Canyon Road. Note: You’ve completed the trifecta of Bruce Lee Trail, Bruce Lee Road and Bruce Lee Spring Trail. These were named not after the legendary martial artist but after the past president of the Concord Mount Diablo Trail Ride Association, the equestrian association that sold 350 acres to Mount Diablo State Park in the 1960’s, much of which you will have explored on this hike. Bruce Lee Spring Trail by Steve Smith Bruce Lee Spring Trail by Steve Smith Coulter Pond by Steve Smith Donner Hike Map BACK TO LIST

Ruby-crowned Kinglet 2024-01-01 by Dan Sandri Dan Sandri Hey! What’s that small, seemingly-restless bird, on the move through the tree branches, making rapid chipping sounds and flicking its wings? It’s there… but then it isn’t… It may be one of our most active Mount Diablo Winter residents: a Ruby-crowned Kinglet (Corthylio calendula). A Ruby-crowned Kinglet is an olive-green and golden-colored bird, with a prominent white eye ring, white wingbar and very small, thin bill. This wingbar contrasts with a black bar on the wing, which helps differentiate it from the similar-looking, but a bit larger, Hutton’s Vireo (Hutton’s Vireos also have a more-conical bill). The “ruby crown” possesed by the male is only occasionally visible, when the bird is agitated or excited, especially in Spring. In Summer, Ruby-Crowned Kinglets have migrated to the north or northeast and are common in conifer and mixed forests in the northwestern United States and across Canada. Ruby-Crowned Kinglets nest high in trees, and therefore in this season prefer taller, older trees. During migration and in Winter, they are common in woods and thickets across most of the continent. Ruby-Crowned Kinglets prey on spiders and many types of insects, foraging in tree foliage, flitting about, hovering and pecking in in their search for food. These birds also eat a small amount of seeds and fruit, including poison-oak berries. So keep an eye out for this Kinglet – or an ear for their chatter, as they are often heard first. Tis the season! Bird Guide: https://www.mdia.org/birds-1-1/ruby-crowned-kinglet Ruby-crowned Kinglet (Corthylio calendula)1 Dan Sandri.jpeg BACK TO LIST

Edwards Digger Bee, and Its Nemesis 2025-03-16 Spring brings Bees! by Dan Sandri Spring brings the Digger Bees (Genus Anthophora ) out of the ground as they emerge from the nests prepared by female bees the year before. One of the Diggers with the largest, most active aggregations in Mount Diablo State Park is the Edwards Digger Bee, and they begin to emerge in late February and early March. The males emerge first and begin noisily patrolling the nesting areas (often a wide fire trail, such as Old Finley Road or Burma Road). The females emerge next and, after mating, begin to dig tunnels. A female will construct a single nest cell at the end of this tunnel, about 3-4 inches down, and fill it with a nectar-pollen mixture, upon which they lay a single egg. She then seals the nest and gets to work on another one. Her larva will feed on the nest provisions and pupate in the fall. Adults hatch in the fall, but stay underground until the following February/March. Alas, it doesn’t always go smoothly for the Edwards Digger Bee. In addition to parasitic threats posed by Bee Flies (Family Bombyliidae), Miltogrammine Flies (Subfamily Miltogramminae, Family Sarcophagidae), Cuckoo Wasps (Family Chrysididae) and other insects, there may be a Lovely-Tailed Mourning Bee (Melecta separata callura ) lurking nearby. The Lovely-Tailed Mourning Bee is a medium-large, strikingly beautiful bee, but with a life history that is adversarial to that of Anthophora Digger Bees. It will seek out a completed nest, dig it out, and lay her own egg in the nest cell. Its larva will hatch first and will eat the egg of the host bee and any other parasite eggs, and eat the pollen contents of the nest. The larva then pupates in the nest cell, and will emerge the following year. Edwards Digger Bee (Anthophora edwardsii) Lovely-tailed Mourning Bee (Melecta separata ssp. callura) on Redmaids (Calandrinia menziesii) BACK TO LIST

Tarantulas on Mount Diablo 1998-10-01 Mike Woodring Why are tarantulas out wandering about? Late summer and fall is tarantula time on Mount Diablo. The tarantula (Aphonopelma sp.), North America’s largest spider, is nocturnal and spends most of its life in and around its underground burrow. However, when a male tarantula reaches maturity at about four to seven years of age, he sheds his exoskeleton for the last time, develops little spurs or hooks on his front legs, and leaves his subterranean home for good to risk life and limb (all eight of them) in search of females of his species with which to mate. These males are the autumnal wanderers we see on the mountain. After a male locates a female by scent, he gently taps at the entrance to entice her out of her burrow to mate. He uses the small clasping hooks on his front legs to hold her fangs and bend her backward. Mating lasts from 30 seconds to a couple of minutes. After mating, the larger, longer lived female (she may live to the ripe old age of 20 years or more) returns to her burrow, ultimately to hatch a hundred or so baby spiders the following spring, of which perhaps one or two spiders will survive to adulthood. It’s not easy being a tarantula. Will a female tarantula eat the male? It’s a myth that female tarantulas always kill the males after mating. On rare occasions, a female that has already mated several times and is approached by an amorous male may attack and eat the male rather than mate again. A female may consume the male if she is famished and needs a meal to be able to lay eggs, but almost always she allows the male to retreat to continue searching for other females until he succumbs to the elements in a few weeks, due to the onset of cold weather, starvation, or the jaws of a predator. Note to parents: A wandering tarantula won’t live long enough to make a good pet. What do tarantulas eat? Typically, a hunting tarantula waits patiently in its burrow near the opening until an unsuspecting insect (usually a cricket) crawls by. The spider rushes out, bites the prey, and drags its victim back into the burrow. In the dark of night, this activity goes unnoticed (except by the cricket!). Why do some tarantulas have a bald spot? The tarantula’s main weapon against larger creatures is defensive. If a bobcat or fox is harassing it, the spider rises up on its front legs and with its back legs scrapes off a cloud of barbed, porcupine-like hairs from its abdomen into the nasal passages and mucous membranes of its tormentor. This tactic sometimes gives the tarantula time to escape and is why a tarantula may sport a bald spot on its abdomen. Who is its most feared predator? The large black and orange female tarantula hawk wasp (Pepsis sp.) seeks out and attacks the tarantula. After delivering a paralyzing sting under a leg, the wasp drags the tarantula to a hole and, before covering the tarantula, she lays a single egg on the helpless spider. When the egg hatches, the young wasp larva eats the tarantula alive. How bad is a tarantula’s bite? Despite its fearsome appearance and formidable reputation, the tarantula is really a rather innocuous creature–a terror to small insects and not much else! Tarantulas have very small venom glands, and its very mild venom is only strong enough to paralyze a cricket, with practically no effect on people. Mount Diablo’s tarantulas are really gentle souls that play an important part in the web of life on our island mountain. So the next time you encounter a tarantula on the trail, remember the old adage, “If you wish to live and thrive, let a spider run alive!” Download Tarantulas: Protect These Gentle Giants Brochure (pdf) BACK TO LIST