Blog: Whitewater Canyon

CabezonDinosaur02COPY
The mouth of the Whitewater River is seven miles east of the Jurassic fauna at Cabezon.

The Whitewater River is the principal drainage for the southeastern portion of the San Bernardino Mountains. It debouches into San Gorgonio Pass where it has constructed a large, side entry alluvial fan. Strong west winds blow down the pass across the fan, pick up sand and dust, and carry them down the trough into North Palm Springs, sand blasting automobiles making their way up the pass on I-10.

Take exit 114 off I-10 near Cabezon to explore Whitewater Canyon. At the mouth of the canyon an outlet sells decorative building stone obtained from two quarries upstream. The stone is gneiss and schist used for building facings, patios, walls, fireplaces, and other masonry work. Colorful decorative gravel, locally called Palm Springs Gold and obtained from another quarry, is a beautiful mix of white quartz, violet mica schist, pink piemontite, and various hydrothermally altered orange and reddish-brown rocks. These minerals and rocks are derived from metamorphic rocks farther upstream in the heart of the San Bernardino Mountains.

From the mouth of the wash proceed north and upstream along a two-lane road about 1 mile through sparse desert vegetation, until you abruptly encounter an oasis of lush vegetation in the bottom of the wash. The oasis marks the trace of the Coachella Valley–Banning fault, which strikes nearly east across the canyon, placing Cabazon fanglomerate of late Pleistocene age on the downstream side of the fault against gneiss and granite of Proterozoic age on the upstream side. The oasis is located where subsurface water percolating southward through canyon alluvium is dammed by impervious clay fault gouge along the fault. The water table is thus higher on the upstream side of the fault, so that springs flow at the surface and water the oasis.

The Whitewater fault lies within the east canyon wall, almost parallel to the canyon, and juxtaposes old alluvium against Coachella fanglomerate of late Miocene age. You can view a splendid exposure of the fanglomerate at the terminus of the road adjacent to a trout farm about 5 miles from the mouth of the canyon.

S007_WhitewaterCongCOPY
Coachella fanglomerate contains some unique clast types, including slightly metamorphosed granite with large crystals of potassium feldspar. The granite closely resembles that in the Cargo Muchacho Mountains near the Mexican border – a suggested correlation that requires 135 miles of right-slip along the San Andreas fault since deposition of the fanglomerate in Miocene time.            (33° 59.5N, 116° 39.4W)

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Southern California Geology in the News

20 May 2016: “World’s largest solar plant catches fire” – blog by Linda Kratachwill

10 May 2016: “Is the San Andreas fault ‘locked, loaded, and ready to go’?” – blog by Temblor.net

4 May 2016: “San Andreas fault “locked, loaded and ready to go with big earthquake” – originally published by Los Angeles Times

23 April 2016:  “Saving the Salton Sea”  –   originally broadcast by KCET

21 April 2016:   “Imperial seismic swarm lights up the southern tip of the San Jacinto fault in an area of extreme hazard”

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Blog: CA 58 – Bakersfield to Tehachapi

Posted 22 April 2016 by A. G. Sylvester ©

MaricopaBasin16D22
Generalized geologic map of southern San Joaquin Valley and Tehachapi Mountains, after Goodman and Malin (1992) with modifications.        Map prepared by Libby Gans ©

 

Southern San Joaquin Basin

The southern San Joaquin basin is a prolific oil-producing area that has had a complex tectonic and depositional history. It originated as the southern part of a large forearc basin in late Mesozoic time, was affected by both shortening and extensional tectonics in Paleogene time, and underwent a final episode of subsidence and infilling during Neogene time under the influence of strike-slip deformation associated with the North American-Pacific plate boundary. During Neogene time, thick diatomaceous oil-prone source rocks of upper Miocene Monterey Formation were deposited in the southern part of the basin. They underwent subsidence and diagenesis, and generated large volumes of hydrocarbons. Numerous and thick sandstone bodies are interbedded with the diatomaceous strata and form the main reservoirs. Shelfal clastic units surround the basin on the east, south, southwest, and north. Large submarine canyons were cut across the shelves, probably during low sea level periods, and funneled sand basinward, where thick, sand-rich, submarine fans accumulated.

During Pliocene time, shallow-marine and intertidal conditions prevailed throughout the basin, because it was gradually cut off from the Pacific Ocean. During Pleistocene time, thick nonmarine strata were deposited in the basin, dominated by fluvial, lacustrine, alluvial-fan, and fan-delta depositional systems of the Tulare Formation and related units. The basin continues to undergo subsidence in its axial portions, concurrently with uplift along the western, southern, and eastern margins.

At least 40,000 feet of marine and terrestrial sedimentary rocks in the Maricopa sub basin are visible only in drill cuttings from the hundreds of boreholes that have punched the basin in the relentless search for oil and gas. The many pumpjacks along the route attest to the number and success of the drill holes. The drill cores may be studied at the California Well Sample Repository in Bakersfield.

The Maricopa sub basin lies upon metaigneous rocks that represent subsurface equivalents of ensimatic and ultramafic rocks that are exposed along the west side of the Sierra Nevada batholith and probably represent the floor of the batholith. The floor of the shallower Tejon embayment, by contrast, is crystalline granite, diorite or gneissic rock regarded as subsurface projections of exposed meta-tonalite and gneiss in the Tehachapi Mountains.

The oldest sedimentary rocks in the Maricopa sub basin are mid-Eocene shallow marine sandstone, siltstone, and shale beds that are overlain by Oligocene and Miocene volcanic rocks, coarse sandstone, and various conglomerates that interfinger with well-sorted, fine-medium grained marine sandstone and shale. The lower Miocene volcanic rocks have been dated at 22.7 million years and include a thick stacked sequence about 2,000 feet of basalt and dacite lava flows, lapilli and lithic tuff, volcaniclastic units, rhyodacite breccia, and dikes. The volcanic rocks are overlain by a very thick sequence of various shallow and deep water marine facies of sandstone, shale, and Monterey Shale of mid-Miocene age. Pliocene and Pleistocene deposits are represented by coarse alluvial fan and fluvial sediments, which interfinger with shallow marine shelf, brackish-water, and lacustrine deposits in the center of the basin. These basin center deposits indicate a gradual shoaling of the basin. The entire sedimentary succession contains major and minor unconformities, lateral and vertical facies changes, and is cut by various major and minor faults, all of which attest to the complex history of basin subsidence, deposition, and deformation of a huge pile of rocks that lie “under the rug” of the valley floor.

From Bakersfield to General Beale Road (Exit 127), the flatness of CA 58 belies the complex geology beneath Quaternary fluvial gravel and sand. North of the highway are dissected hills consisting of the Kern River Gravel, a non-marine, clastic, loosely consolidated, west-dipping alluvial fan sequence deposited not by the Kern River where it debouches into the valley, but instead by the now abandoned Caliente River (Saleeby et al, 2013). The deposits contain sand, pebble-sized gravel, rounded to sub-rounded cobbles and boulders, consisting of various igneous and metamorphic rocks, all derived from the core and west flank of the Sierra Nevada.

Tehachapi Mountains

Basinal marine strata interfinger with alluvial fan debris shed from the adjacent Tehachapi Mountains. The latest of these fans lies upon the valley floor close to the mountains. Some of them are dissected and are expressed by low hills before steep gradient of the highway begins.

BealvilleMap
Generalized geology map of the Bealville area, after Dibblee and Chesterman (1953) with modifications. Map prepared by Libby Gans ©

The Bealville Fanglomerate is one of the older alluvial fan deposits in the Bakersfield area and provides the earliest evidence of strong uplift of the area east or southeast of the south end of the present San Joaquin Valley. Its age is regarded as late Oligocene and early Miocene based on stratigraphic relations. The formation consists of a light-gray, loosely consolidated mass of unsorted granitic detritus, with semi-rounded boulders of quartz diorite up to three feet in diameter. It nonconformably overlies granitic and meta-tonalitic basement and is more than 7,000 feet thick at Bealville. Most of the roadcuts farther up the grade from Keene (Exit 139) to Tehachapi expose granitic rocks – rarely foliated hornblende-biotite quartz diorite with hornblendite and gabbro in small irregular and linear masses. In the 3-5 miles before Tehachapi, mica schist and marble lenses are in the quartz diorite.

CA 58 crosses the Edison fault, which separates quartz diorite and Bealville Fanglomerate about two miles east of General Beale Road (Exit 127). It also crosses the White Wolf fault, source of the 1952 Arvin-Tehachapi earthquake (M 7.7); the fault juxtaposes diorite against diorite near the Bealville turnoff. The Tehachapi Mountains are not only a wall between the south end of the Great Valley and the Mojave Desert, but they also form a lithologic and structural link from the Sierra Nevada to the Transverse Ranges. They are also an impediment to highway and rail traffic. Railroad engineers solved their problem by building the Tehachapi Loop.

 

Tehachapi Loop

CA 58 and the railroad line climb 28 miles out of San Joaquin Valley over Tehachapi Pass to connect the valley with the Mojave Desert. Look for trains passing through tunnels on the south side of the highway. In just two years between 1874 and 1876, up to 3,000 Chinese laborers cut the route through solid and decomposed granite using picks, shovels, horse drawn carts, and blasting powder.

About halfway upgrade to the pass, the world famous Tehachapi Loop spirals 0.73 miles around one of the granite hills. The track climbs a steady 2 percent grade within the loop and passes over itself, thereby lessening the grade. The loop gains 77 feet in elevation, and thus a train more than 4,000 feet long thus passes over itself going around the loop. The average grade is a steep 2.2 percent. It is such a remarkable engineering feat that in 1998 the Loop was named a National Historic Civil Engineering Landmark and is now California Historical Landmark #508.

 

References cited:

Dibblee, T.W., Jr., and Chesterman, C.W., 1953, Geology of the Breckenridge Mountain quadrangle, California: California Division of Mines and Geology Bulletin, no. 168, 56 p., (incl. geologic map, scale 1:62,500).

Goodman, E.D., and P.E. Malin, 1992. Evolution of the southern San Joaquin basin and mid-Tertiary “transitional” tectonics, central California. Tectonics 11, 478-498.

Saleeby, J., Z. Saleeby, and F. Souza, 2013, From deep to modern time along the western Sierra Nevada foothills of California, San Joaquin to Kern River drainages. Geological Society of America Field Guides 32, 37-62. doi: 10.1130/2013.0032(03)

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Blog: I-5 and CA 99 – Grapevine to Bakersfield

Posted 22 April 2016 by A.G. Sylvester ©

MaricopaBasin16D22
Generalized geologic map of the southern San Joaquin basin and the Tehachapi Mountains, after Goodman and Malin (1992). Prepared by Libby Gans ©

 

Southern San Joaquin Basin

The southern San Joaquin basin is a prolific oil-producing area that has had a complex tectonic and depositional history. It originated as the southern part of a large forearc basin in late Mesozoic time, was affected by both shortening and extensional tectonics in Paleogene time, and underwent a final episode of subsidence and infilling during Neogene time under the influence of strike-slip deformation associated with the North American-Pacific plate boundary. During Neogene time, thick diatomaceous oil-prone source rocks of upper Miocene Monterey Formation were deposited in the southern part of the basin. They underwent subsidence and diagenesis, and generated large volumes of hydrocarbons. Numerous and thick sandstone bodies are interbedded with the diatomaceous strata and form the main reservoirs. Shelfal clastic units surround the basin on the east, south, southwest, and north. Large submarine canyons were cut across the shelves, probably during low sea level periods, and funneled sand basinward, where thick, sand-rich, submarine fans accumulated.

During Pliocene time, shallow-marine and intertidal conditions prevailed throughout the basin, because it was gradually cut off from the Pacific Ocean. During Pleistocene time, thick nonmarine strata were deposited in the basin, dominated by fluvial, lacustrine, alluvial-fan, and fan-delta depositional systems of the Tulare Formation and related units. The basin continues to undergo subsidence in its axial portions, concurrently with uplift along the western, southern, and eastern margins.

At least 40,000 feet of marine and terrestrial sedimentary rocks in the Maricopa sub basin are visible only in drill cuttings from the hundreds of boreholes that have punched the basin in the relentless search for oil and gas. The many pumpjacks along the route attest to the number and success of the drill holes. The drill cores may be studied at the California Well Sample Repository in Bakersfield.

The Maricopa sub basin lies upon metaigneous rocks that represent subsurface equivalents of ensimatic and ultramafic rocks that are exposed along the west side of the Sierra Nevada batholith and probably represent the floor of the batholith. The floor of the shallower Tejon embayment, by contrast, is crystalline granite, diorite or gneissic rock regarded as subsurface projections of exposed meta-tonalite and gneiss in the Tehachapi Mountains.

The oldest sedimentary rocks in the Maricopa sub basin are mid-Eocene shallow marine sandstone, siltstone, and shale beds that are overlain by Oligocene and Miocene volcanic rocks, coarse sandstone, and various conglomerates that interfinger with well-sorted, fine-medium grained marine sandstone and shale. The lower Miocene volcanic rocks have been dated at 22.7 million years and include a thick stacked sequence about 2,000 feet of basalt and dacite lava flows, lapilli and lithic tuff, volcaniclastic units, rhyodacite breccia, and dikes. The volcanic rocks are overlain by a very thick sequence of various shallow and deep water marine facies of sandstone, shale, and Monterey Shale of mid-Miocene age. Pliocene and Pleistocene deposits are represented by coarse alluvial fan and fluvial sediments, which interfinger with shallow marine shelf, brackish-water, and lacustrine deposits in the center of the basin. These basin center deposits indicate a gradual shoaling of the basin. The entire sedimentary succession contains major and minor unconformities, lateral and vertical facies changes, and is cut by various major and minor faults, all of which attest to the complex history of basin subsidence, deposition, and deformation of a huge pile of rocks that lie “under the rug” of the valley floor.

 

Wheeler Ridge

Wheeler Ridge, located west of I-5 where it diverges from CA 99, is a splendid example of an actively growing anticline. The fold is so recent that unconsolidated sand and gravel sediments are involved. It is an asymmetric anticline, steep on the north side, with a thrust fault along its northern margin. Several topographic saddles or wind gaps notch the crest of the fold. They were cut across the growing anticline by a stream that flowed north from the San Emigdio Range south of the fold. Eventually the fold grew eastward, like a mouse under a rug, faster than the stream could erode, and so the stream was forced to turn aside and drain progressively around the east end of the growing fold, leaving the older gaps high and dry.  Refer to Sharp and Glazner (1993) for additional information.

 DSC01089
View south of Wheeler Ridge anticline, which plunges from right to left. Four large aqueduct pipes occupy the large wind gap at the west and highest part of the anticline.

1952 Kern County earthquake

One of California’s largest historic earthquakes (M7.5) happened along the southeast edge of the San Joaquin Valley on July 21, 1952. Considerable damage was done to the town of Tehachapi located on the hanging wall block of the fault. It was the largest earthquake to strike California since the 1906 San Francisco earthquake and fire, and the first in California after researchers installed the first generation of seismographs in southern California. Known as the Kern County, or Arvin-Tehachapi earthquake, it occurred on the White Wolf fault, a previously mapped, but undistinguished fault that lies along the south edge of the San Joaquin Valley against the Tehachapi Mountains. Because little surface rupture occurred, it was the seismographic record that produced the most information about the fault, its earthquake, and aftershocks. It turned out that the displacement was reverse, where Bear Mountain in the Tehachapi Mountains was thrust upward about 5 feet and leftward about 4 feet, relative to the floor of the San Joaquin Valley or, more likely, the San Joaquin Valley subsided about 5 feet relative to the Tehachapi Mountains. Over the last 2 million years or so, the vertical displacement along the White Wolf fault has been about 2 to 3 miles; the horizontal separation has not been determined.

References cited:

Goodman, E.D., and P.E. Malin, 1992. Evolution of the southern San Joaquin basin and mid-Tertiary “transitional” tectonics, central California. Tectonics 11, 478-498.
Sharp, R.P., and A.F. Glazner, 1993. Geology Underfoot in Southern California. Mountain Press Publishing Company, Missoula, Montana, pp. 83-87.

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Blog: Salton Sea Sand Dunes

Posted 21 April 2016 by A.G. Sylvester ©

You may gain an up close and personal view of sand dunes near San Felipe Creek, about a mile down a poorly marked and unmaintained side road east of CA 86, 10 miles south of Salton City and about 4 miles north of the Agricultural Inspection Station at the junction of CA 86 and CA 78. The side road terminates at a small field of barchan dunes but it once continued to a dormant U.S. Navy testing base on the edge of the Salton Sea. The road is paved but do not drive onto the sand or your vehicle will get stuck when you park or turn around! The testing facility itself is off-limits to the public.

DSC00569
“Soft Sand by the Salton Sea” Original oil painting by Robin Gowen©

Barchan dunes are crescent-shaped with a long, gentle back slope and a steep frontal slope that is horn-shaped.  Individual barchans are 25 to 100 feet across and six to 30 feet high. In front of the dune is bare ground with some pebbles and vegetation that will be buried eventually as the dune advances. If you happen to be there when a gentle wind is blowing, you will see sand struggling up the rippled back slope and then cascading down the frontal slope. The horns advance almost imperceptibly. Look also for tracks in the sand made by lizards, stink bugs, and the occasional sidewinder.

The horns of barchan dunes point and migrate in the direction of the prevailing wind. The crescents of these dunes point east, indicating a prevailing west wind. They move eastward about 50 to 80 feet per year to their ultimate demise in the Salton Sea. The mineralogy of the sand indicates that the bulk of the sand comes from the poorly consolidated and easily weathered Cenozoic sedimentary strata in the hills west of CA 86. Lesser amounts come from nearby stream washes.

 S013_BarchanDuneCOPY The Salton barchan dunes are located below the high-water level of old Lake Cahuilla, so the dune field is probably less than 400 years old. (33° 10.9N, 115° 51.1W)

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Blog: CA 1 – Lompoc to Guadalupe

Posted 21 April 2016 by A.G. Sylvester ©

CA 1 proceeds west and then north through Lompoc on the Santa Ynez River flood plain. CA 1 crosses the Santa Ynez River about two miles north of the center of town, then climbs upon the broad, chaparral-covered Burton Mesa and heads west to the main gate of Vandenberg Air Force Base. The mesa consists of the Orcutt Sand, a deposit of tan to rusty brown, friable to locally indurated wind-blown sand interbedded with gravel covering a large area between Lompoc and Santa Maria. Gullies notch the plain and expose outcrops of diatomaceous mudstone of the Pliocene Sisquoc Formation and of siliceous shale and porcelanite of the Monterey Shale.

Northward from the Vandenberg AFB gate (PM 28.6), the highway passes across 4 miles of locally deformed Orcutt Sand, being tilted as much as 12 degrees on the flanks of anticlines. The maximum outcrop thickness of the Orcutt Sand is between 50 and 100 feet throughout the Santa Maria area. It is eroded into badlands at the intersection with Firefighter Road (RM 29.9). CA 1 descends the long Harris Grade into San Antonio Valley and Barka Slough (PM 37.1) to Pliocene Sisquoc Formation at the base of the grade.

The low rolling hills on both sides of the highway between Barka Slough and Guadalupe are parts of an extensive series of stacked longitudinal sand dunes of Late Pleistocene to Recent age. Prevailing northwest winds carried the sand inland from coastal beaches.

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