GeoTrek IV-B

GEOTREK IV-B
EASTERN SANTA MONICA MOUNTAINS

Wednesday, February 23, 2011

Topic: Mesozoic plutonic and Neogene sedimentary, volcanic, and structural history of the eastern Santa Monica Mountains.

Participants: Bob Ableson, Robinson Cecil, Gene Fritsche, Sue Fritsche, Dick Heermance, Carolyn Milkovich, and George Milkovich. See the first photo below (the group photo) to pick out these people.

Distance and Route: We went about 9.8 miles, on a counterclockwise circular route in Griffith Park along the following trails: Old Zoo Trail, Eckert Trail, Vista del Valle Dr., Mount Hollywood Dr., Western Canyon Rd., Lower West Observatory Trail, Vermont Canyon Rd., Aberdeen Trail, past Vista del Valle Dr., and back to the parking area on Fern Canyon Trail. See Google Earth route map below.

Profile: On the profile below the start of the hike is on the left end. Elevation gain was 1,769 feet; because the route was circular the elevation loss was the same 1,769 feet.

Geology: The hike was on the Dibblee Hollywood-Burbank (South 1/2) quadrangles (DF-30). Formations seen included Cretaceous granodiorite and quartz diorite plutons, middle Miocene volcanics and interbedded sedimentary rocks, the middle Miocene Calabasas(?) Formation, and the upper Miocene Monterey Formation. Depositional environments, stratigraphic problems, and structural history of the area were discussed along the trail.

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

GeoTrek IV-B in Griffith Park attracted 7 participants. From left to right they are Gene Fritsche, Bob Ableson, Dick Heermance, Carolyn Milkovich, George Milkovich, Robinson Cecil, and the photo taker Sue Fritsche. Tagging along for the outing was Henry.
Dick Heermance studies a trail exposure of conglomerate in the middle Miocene Calabasas Formation.
Closeup of the conglomerate of the middle Miocene Calabasas Formation. Cobbles are subrounded, indicating a moderate distance of transport before deposition. The cobbles consist of granitoid rocks, quartzite, gneiss, and metavolcanic rocks.
Roadcut through the lower Miocene Conejo Volcanics, which in this exposure consists of basalt flow rocks.
Spheroidal weathering in the lower Miocene Conejo Volcanics, which in this exposure is an andesitic basalt.
The Conejo Volcanics in the bottom of the photo are interbedded with the sandstone deposits seen at the top of the photo. The sandstone was deposited on the Conejo lava flows in between eruptive events. Both are of early Miocene age. Dibblee refers the sandstone to the Middle Topanga Formation.
Roadcut exposure of sandstone in the lower Miocene Middle Topanga Formation. These sandstone beds contain shallow-marine fossils that indicate deposition in a shallow ocean environment.
Closeup view of a conglomeratic coarse-grained sandstone in the lower Miocene Middle Topanga Formation.
Large vertebrate bone fragment in the lower Miocene Middle Topanga Formation. The invertebrate fossils in the formation indicate that it was deposited in the ocean, so the bone most likely came from a large marine mammal like a whale.
Closeup of the igneous intrusive quartz diorite exposed in Griffith Park. Note the moderate amount of small black minerals in the rock that give it a medium gray color which distinguishes it from the other intrusive rock in the park shown in the next photo.
Closeup of the igneous intrusive granodiorite exposed in Griffith Park. Compared to the previous photo, note the lesser amount of small black minerals in the rock and the light gray color.
We had lunch in the Fern Dell area of Griffith Park. We were famished by the time we got there and our lunch was yummy.
Hiking up the trail southwest of the Griffith Observatory. All the rocks in this area are granodiorite.
Questions involving the intrusive igneous rocks were sometimes beyond Gene's knowledge, so we all benefitted from Robinson's explanation.
Trailcut exposures of granodiorite below the Griffith Observatory.
Trailcut exposure of granodiorite just underneath the Griffith Observatory.
Closeup of the granodiorite just underneath the Griffith Observatory. Note the minor amount of small black minerals and the light gray color.
Granodiorite enhanced by a bunch of morning glories.
Granite dikes (light gray) intruding granodiorite. The granite was intruded into the granodiorite along fractures and is younger than the granodiorite. Note also the lighter gray color and the lesser amount of small black minerals in the granite.
As we neared the end of the hike, we stopped for an overview of the Los Angeles basin. Los Angeles skyscrapers are in the left-center of the photo and the Palos Verdes Hills on the right horizon.
Heading down the homestretch. The gray spot in the center of the photo is the parking lot where our cars were parked. Glendale is in the midground and the San Gabriel Mountains are in the background.

Return to the GeoTrek IV index.
THIS PAGE LAST MODIFIED ON JUNE 14, 2011
If you have questions or comments, you may leave a message at:
geneandsuef@dslextreme.com

	GeoTrek IV-B in Griffith Park attracted 7 participants. From left to right they are Gene Fritsche, Bob Ableson, Dick Heermance, Carolyn Milkovich, George Milkovich, Robinson Cecil, and the photo taker Sue Fritsche. Tagging along for the outing was Henry.
	Dick Heermance studies a trail exposure of conglomerate in the middle Miocene Calabasas Formation.
	Closeup of the conglomerate of the middle Miocene Calabasas Formation. Cobbles are subrounded, indicating a moderate distance of transport before deposition. The cobbles consist of granitoid rocks, quartzite, gneiss, and metavolcanic rocks.
	Roadcut through the lower Miocene Conejo Volcanics, which in this exposure consists of basalt flow rocks.
	Spheroidal weathering in the lower Miocene Conejo Volcanics, which in this exposure is an andesitic basalt.
	The Conejo Volcanics in the bottom of the photo are interbedded with the sandstone deposits seen at the top of the photo. The sandstone was deposited on the Conejo lava flows in between eruptive events. Both are of early Miocene age. Dibblee refers the sandstone to the Middle Topanga Formation.
	Roadcut exposure of sandstone in the lower Miocene Middle Topanga Formation. These sandstone beds contain shallow-marine fossils that indicate deposition in a shallow ocean environment.
	Closeup view of a conglomeratic coarse-grained sandstone in the lower Miocene Middle Topanga Formation.
	Large vertebrate bone fragment in the lower Miocene Middle Topanga Formation. The invertebrate fossils in the formation indicate that it was deposited in the ocean, so the bone most likely came from a large marine mammal like a whale.
	Closeup of the igneous intrusive quartz diorite exposed in Griffith Park. Note the moderate amount of small black minerals in the rock that give it a medium gray color which distinguishes it from the other intrusive rock in the park shown in the next photo.
	Closeup of the igneous intrusive granodiorite exposed in Griffith Park. Compared to the previous photo, note the lesser amount of small black minerals in the rock and the light gray color.
	We had lunch in the Fern Dell area of Griffith Park. We were famished by the time we got there and our lunch was yummy.
	Hiking up the trail southwest of the Griffith Observatory. All the rocks in this area are granodiorite.
	Questions involving the intrusive igneous rocks were sometimes beyond Gene's knowledge, so we all benefitted from Robinson's explanation.
	Trailcut exposures of granodiorite below the Griffith Observatory.
	Trailcut exposure of granodiorite just underneath the Griffith Observatory.
	Closeup of the granodiorite just underneath the Griffith Observatory. Note the minor amount of small black minerals and the light gray color.
	Granodiorite enhanced by a bunch of morning glories.
	Granite dikes (light gray) intruding granodiorite. The granite was intruded into the granodiorite along fractures and is younger than the granodiorite. Note also the lighter gray color and the lesser amount of small black minerals in the granite.
	As we neared the end of the hike, we stopped for an overview of the Los Angeles basin. Los Angeles skyscrapers are in the left-center of the photo and the Palos Verdes Hills on the right horizon.
	Heading down the homestretch. The gray spot in the center of the photo is the parking lot where our cars were parked. Glendale is in the midground and the San Gabriel Mountains are in the background.