GeoTrek IV-E

GEOTREK IV-E
WESTERN SANTA MONICA MOUNTAINS

Saturday, March 12, 2011

Topic: Cenozoic sedimentary, volcanic, and structural history of the western Santa Monica Mountains.

Participants: Monica Carlson, Gene Fritsche, Sue Fritsche, Connie Hanstedt, Pam Irvine, Dennis Keating, Kathleen Keating, John Klutke, Carolyn Milkovich, George Milkovich, Jonathan Miller, Syrus Parvizian, Christiaan Patterson, Vicki Pedone, Martha Sgriccia, Bryan Swanson, Mike Tacsik, and Diana Woody. Sue Fritsche took the photo. See the first photo below (the group photo) to pick out these people.

Distance and Route: About 9.6 miles, mostly in Malibu Creek State Park, along the following trails: Phantom Trail, Cistern Trail, Lookout Trail, Crags Road, Bulldog Motorway, Castro Motorway, and Corral Canyon Road. See Google Earth route map below.

Profile: On the profile below the start of the hike is on the left end. Elevation gain was 2,695 feet; elevation loss was 1,675 feet.

Geology: The hike began on the Dibblee Calabasas quadrangle (DF-37), moved to the Dibblee Malibu Beach quadrangle (DF-47), and finished on the Dibblee Point Dume quadrangle (DF-48). Formations we saw include the Paleocene Santa Susana Formation, the Eocene Llajas Formation, and the Miocene Topanga Canyon Formation, Conejo Volcanics and associated sedimentary rocks, intrusive diabase, and Monterey Formation. Depositional environments, stratigraphic problems, and structural history of the area will be reviewed. At the end of the hike we will see and discuss the most complex problem in the Santa Monica Mountains, the Malibu Bowl fault.

PHOTOS TAKEN IN THE WESTERN SANTA
MONICA MOUNTAINS ON GEOTREK IV-E
Photos taken by Gene Fritsche.
Click on the small picture to see an enlargement.

A hearty group of hikers, eager to begin GeoTrek IV-E, gathers at the Liberty Canyon trailhead ready for their hike through Malibu Creek State Park.
After a short walk on the Liberty Canyon Trail, we switched to the Phantom Trail where lots of trees provided some cool shade.
Halfway along the Phantom Trail we paused to look for a contact, or was it a contact lens? The grassy area here is all underlain by the Monterey Formation.
Small exposure along the Phantom Trail of thin-bedded, siliceous shale belonging to the upper Miocene Monterey Formation.
Two California golden poppies, the state flower of California, growing along the Phantom Trail.
As we continued along the Phantom Trail we started to spread out a little bit, but were still recognizable as part of one group.
In addition to poppies, we also found paintbrush producing vivid red colors along the sides of the Phantom Trail.
Where the Phantom Trail meets Mulholland Hwy., the upper Miocene Monterey Formation contains thick sandstone beds. These sandstone beds contain sedimentary structures indicative of deposition by turbidity currents and submarine slides in rather deep ocean water. Where sandstone and shale beds are intermixed like this, the rock unit is commonly called the Modelo Formation.
We hiked south from Mulholland Hwy. on the Cistern Trail. This view is looking west from the Cistern Trail into a small valley. Goat Buttes, on the left side of the photo, are made of basalt belonging to the lower Miocene Conejo Volcanics.
Here we are on the Lookout Trail with Goat Buttes on the right background.
The Monterey Formation is exposed along the north side of Crags Road as we proceed west in the valley formed by Malibu Creek.
A typical exposure of the thin-bedded, siliceous Monterey Formation as it is exposed along the north side of Crags Road in Malibu Creek valley.
We had lunch at the MASH site in Malibu Creek State Park. Goat Buttes, in the background, are made of basalt lava flows belonging to the lower Miocene Conejo Volcanics.
We gathered for a second group photo around the MASH ambulance, an important part of the TV series.
Group studies the lower Miocene, shallow-marine sandstone of the Topanga Canyon Formation along the Bulldog Motorway.
A scallop fossil in the lower Miocene Topanga Canyon Formation. This particular species of fossil scallop identifies the age of the formation and the small pebbles in the rock prove that it was deposited in shallow water just below the ocean shoreline.
A sand dollar fossil in the lower Miocene Topanga Canyon Formation. This particular species of fossil sand dollar, like the previous scallop, identifies the age of the formation. As more and more sand was deposited around and above the sand dollar, the sand was packed tightly. Later the actual shell of the sand dollar dissolved to leave a hole where the shell had been. Even though the shell is missing, this mold of the shell is still considered a fossil.
Two marine animal burrows, perhaps shrimp burrows, in the lower Miocene Topanga Canyon Formation. The animal digs the burrow in which it lives (now filled with the lightest colored sand). Fecal material expelled while the animal is in the burrow is packed against the walls of the burrow to make them smooth (the brown rim around the light colored sand). When the animal permanently leaves the burrow, it fills in with sand. Note that the light colored sand filling the burrow is slightly coarser than the medium brown sand surrounding the burrow.
Roadcut exposure of the lower Miocene Topanga Canyon Formation (above) that has been intruded by a dike of lower Miocene igneous rock called diabase (below). Diabase has the same composition as basalt, but is intrusive, hence cools more slowly and contains larger crystals than the extrusive lava flows of basalt.

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THIS PAGE LAST MODIFIED ON JUNE 24, 2011
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	A hearty group of hikers, eager to begin GeoTrek IV-E, gathers at the Liberty Canyon trailhead ready for their hike through Malibu Creek State Park.
	After a short walk on the Liberty Canyon Trail, we switched to the Phantom Trail where lots of trees provided some cool shade.
	Halfway along the Phantom Trail we paused to look for a contact, or was it a contact lens? The grassy area here is all underlain by the Monterey Formation.
	Small exposure along the Phantom Trail of thin-bedded, siliceous shale belonging to the upper Miocene Monterey Formation.
	Two California golden poppies, the state flower of California, growing along the Phantom Trail.
	As we continued along the Phantom Trail we started to spread out a little bit, but were still recognizable as part of one group.
	In addition to poppies, we also found paintbrush producing vivid red colors along the sides of the Phantom Trail.
	Where the Phantom Trail meets Mulholland Hwy., the upper Miocene Monterey Formation contains thick sandstone beds. These sandstone beds contain sedimentary structures indicative of deposition by turbidity currents and submarine slides in rather deep ocean water. Where sandstone and shale beds are intermixed like this, the rock unit is commonly called the Modelo Formation.
	We hiked south from Mulholland Hwy. on the Cistern Trail. This view is looking west from the Cistern Trail into a small valley. Goat Buttes, on the left side of the photo, are made of basalt belonging to the lower Miocene Conejo Volcanics.
	Here we are on the Lookout Trail with Goat Buttes on the right background.
	The Monterey Formation is exposed along the north side of Crags Road as we proceed west in the valley formed by Malibu Creek.
	A typical exposure of the thin-bedded, siliceous Monterey Formation as it is exposed along the north side of Crags Road in Malibu Creek valley.
	We had lunch at the MASH site in Malibu Creek State Park. Goat Buttes, in the background, are made of basalt lava flows belonging to the lower Miocene Conejo Volcanics.
	We gathered for a second group photo around the MASH ambulance, an important part of the TV series.
	Group studies the lower Miocene, shallow-marine sandstone of the Topanga Canyon Formation along the Bulldog Motorway.
	A scallop fossil in the lower Miocene Topanga Canyon Formation. This particular species of fossil scallop identifies the age of the formation and the small pebbles in the rock prove that it was deposited in shallow water just below the ocean shoreline.
	A sand dollar fossil in the lower Miocene Topanga Canyon Formation. This particular species of fossil sand dollar, like the previous scallop, identifies the age of the formation. As more and more sand was deposited around and above the sand dollar, the sand was packed tightly. Later the actual shell of the sand dollar dissolved to leave a hole where the shell had been. Even though the shell is missing, this mold of the shell is still considered a fossil.
	Two marine animal burrows, perhaps shrimp burrows, in the lower Miocene Topanga Canyon Formation. The animal digs the burrow in which it lives (now filled with the lightest colored sand). Fecal material expelled while the animal is in the burrow is packed against the walls of the burrow to make them smooth (the brown rim around the light colored sand). When the animal permanently leaves the burrow, it fills in with sand. Note that the light colored sand filling the burrow is slightly coarser than the medium brown sand surrounding the burrow.
	Roadcut exposure of the lower Miocene Topanga Canyon Formation (above) that has been intruded by a dike of lower Miocene igneous rock called diabase (below). Diabase has the same composition as basalt, but is intrusive, hence cools more slowly and contains larger crystals than the extrusive lava flows of basalt.