GeoTrek IV-K

GEOTREK IV-K
SOLEDAD BASIN

Saturday, May 28, 2011

Topic: Neogene sedimentary history of the Soledad Basin and age of the San Gabriel Mountains. Traverse from Soledad Canyon to Vasquez Rocks County Park.

Participants: Gene Fritsche, Sue Fritsche, Kayla Kilpatrick, RJ Kipatrick, Kris Kittleson, Daniel McCarty, Ryan McCarty, Syrus Parvizian, Vicki Pedone, Tony Reid, Jane Rollins, Lynn Sosa, and Doug Yule. See the first photo below (the group photo) to pick out these people.

Distance and Route: Total distance was about 9.0 miles along the Pacific Crest Trail. See Google Earth route map below.

Profile: On the profile below the start of the hike is on the left end. Total elevation gain was 1,828 feet and total elevation loss was 1,596 feet.

Geology: The hike is on the Dibblee Agua Dulce quadrangle (DF-58). Formations we saw included Precambrian anorthosite and schist, Mesozoic granite, and the upper Eocene to lower Miocene Vasquez Formation sedimentary and volcanic rocks. We also saw the Agua Dulce Fault. Depositional environments, stratigraphic problems, and structural history of the area will be reviewed. Also we saw evidence for the age of the San Gabriel Mountains.

PHOTOS TAKEN IN THE SOLEDAD BASIN ON GEOTREK IV-K
Photos taken by Gene Fritsche, Jane Rollins, and Doug Yule.
Click on the small picture to see an enlargement.

Group photo at the start of the hike on the Pacific Crest Trail where it crosses Soledad Canyon. It was a beautiful day and we were eager to get on the trail.
The hike started in the plutonic igneous rocks of the San Gabriel Mountains. Our authority on the subject was Doug Yule who provided us an overview of the important San Gabriel Mountains rocks.
Soon after starting we had to cross the Santa Clara River. Luckily the river was only creek size and crossing was easy. In this photo, Lynn Sosa is followed across the creek by Syrus Parvizian.
Here's Sue Fritsche crossing the boards that took us across one of the channels of the Santa Clara River.
Tony Reid is followed by Doug Yule across the creek. No one fell in, so it was a successful crossing.
Soon after crossing the Santa Clara River we came to the north bank of Soledad Canyon, location of the main railroad line between Los Angeles and the Antelope Valley. We stopped, looked, and listened before crossing.
After climbing up the trail a ways, we came to a small outcrop where Gene stopped to talk about the rocks that were exposed.
Trailcut exposure of soft, clayey weathered anorthosite. Anorthosite is made mostly of calcium-rich plagioclase feldspar which weathers rather rapidly to clay minerals when exposed to weathering elements on the earth's surface. Dating of unweathered samples of anorthosite from the San Gabriel Mountains shows that the anorthosite is 1.2 billion years old.
Dike of weathered anorthosite intruding an older schist. The intruded schist in other parts of the San Gabriel Mountains is estimated to be around 1.7 billion years old.
Dike of granite intruding the schist. The granite, if related to other granites in the San Gabriel Mountains, is most likely Mesozoic in age.
Hiking along the Pacific Crest Trail just after crossing the Soledad Fault.
A trailcut exposure of the Oligocene-Miocene Vasquez Formation is studied by the group. Gene gets them to describe the features that they see.
Gene takes one of the many photos that make up this report. Go to next photo to see the result.
Closeup view of an Oligocene-Miocene Vasquez Formation conglomerate. The angularity of the cobbles and boulders indicates a short distance of transport, and the reddish color is due to nonmarine deposition. The cobbles and boulders are made of anorthosite, gabbro, quartzite and other igneous and metamorphic rocks, some having come from the San Gabriel Mountains and others from farther away. The above features all point to deposition on a rather steep alluvial fan that existed here during the Oligocene and Miocene Epochs. A further conclusion is that the San Gabriel Mountains existed during the Oligocene and that they had already been eroded deeply into the plutonic igneous rocks.
The flattened ridge crests seen in this photo, called stream terraces, are covered with a thin layer of river alluvium that was deposited in a broad river valley that existed here prior to uplift of the area and downcutting of the present stream valleys. The presence of stream terraces indicates that uplift of the area was sporadic, rather than continuous.
The group continues up the Pacific Crest Trail to higher elevations. The San Gabriel Mountains are in the background.
Yellow flowers like these were common along the trail.
This large bush with purple flowers and fuzzy leaves is called Yerba Santa. The native Americans used it for a varity of medicinal purposes.
This outcrop of an Oligocene-Miocene Vasquez Formation conglomerate shows the large size of some of the boulders. Boulders this large could only have been carried down the alluvial fan on which they were deposited by a debris-flow process.
About four different colors of the Mariposa Lily were seen along the trail. This one, of course, is called a Yellow Mariposa Lily.
California Golden Poppies, the California State Flower, had mostly finished their growing season, but there were a few left.
Yucca plants were common along the trail, but only a few of them were blooming like this one.
The light gray outcrops in this photo are exposures of igneous rocks that are surrounded by the Oligocene-Miocene Vasquez Formation. These igneous rocks are not mapped on Dibblee's map of the area.
The group continues along the Pacific Crest Trail through the Oligocene-Miocene Vasquez Formation.
Gene discusses the geologic history of the area, especially the history of the Vasquez Formation. In the background is a resistant outcrop of Vasquez Formation boulder conglomerate that was deposited in an alluvial fan environment.
Gene uses his hands to describe the relationship between bedding in the Vasquez Formation and faults in the area.
The group pauses for a break at the high point on the day's hike. It was mostly downhill from here on.
Heading down into Escondido Canyon which we followed for most of the rest of the hike.
In the center of the photo are exposures of brown, basaltic volcanic rocks that belong to a volcanic member of the Vasquez Formation. These rocks are underneath, hence slightly older, than the conglomerate deposits we had been hiking through previously.
Outcrop of basalt from the volcanic member of the Vasquez Formation that was seen in the last photo. These rocks have been dated radiometrically and produce an age of about 24 million years, which is near the boundary between the Oligocene and the Miocene.
Closeup of the basalt from the volcanic member of the Oligocene-Miocene Vasquez Formation. The blue-green patches are amygdules of an unknown mineral. An amygdule is a bubble hole that has been filled with minerals precipitated from groundwater.
On the left side of the photo the group is hiking on conglomerate of the Vasquez Formation. On the right is an outcrop of basalt of the Vasquez Formation. Passing through the low spot between the two is the Agua Dulce Fault.
We searched quite awhile for a shady spot for lunch and finally found a spot right on the trail where we could settle down in the shade for some nourishment.
Sandwiches, veggies, fruit, cookies, and plenty of liquid were devoured by the group to make sure energy levels were high enough to get through the rest of the day.
As the sun crept into our shady spot, we finished lunch and got ready for the afternoon hike.
We stopped at this outcrop of the Oligocene-Miocene Vasquez Formation because it was a little different from the mostly conglomeratic deposits we had been seeing up to this point. See next photo.
Pebble conglomerate and sandstone beds in the outcrop shown in the previous photo. The Vasquez Formation here is finer grained and better bedded than what we had seen up until this point. These layers were deposited in a river environment, as opposed to the alluvial fan environment of the earlier deposits.
This Prickly Pear cactus with two bright red blossoms really brightened up the trail.
Closeup view of a Prickly Pear blossom.
Pacific Crest Trail tunnel under the Antelope Valley Freeway. It's a good thing that Escondido Creek was not full of water.
Looking through the tunnel. It got rather dark in the middle, but by moving slowly and picking up our feet we made it through without incident.
A short distance from the tunnel, Escondido Creek cuts a deep gorge through the Vasquez Formation. It was cool and shady here.
Sue is smiling because there is only one mile to go.
Resistant cliffs of the Oligocene-Miocene Vasquez Formation tower above the trail in Esondido Canyon.
More Vasquez Formation cliffs along Escondido Canyon.
The trail enters Vasquez County Park and descends into another gorge along Escondido Creek.
We crossed Escondido Creek one more time before entering the final gorge through rocks of the Vasquez Formation.
Excellent example of a debris flow deposit in the Vasquez Formation. The boulders and cobbles in the bed are scattered throughout the bed as would occur in a debris flow deposit, rather than being concentrated near the bottom of the bed as would occur if the bed had been deposited by traction currents in a river or turbidity current. The debris flow bed is about 40 feet thick and was deposited probably in a single day.
Most of the beds in this exposure of the Vasquez Formation are river deposits. Although the thicker bed in the upper left with the pebbles scattered throughout is a small debris flow, the beds below it containing pebbles show that the pebbles are concentrated at the bottom of the bed. This feature is the result of waning traction current deposition by rivers.
Exiting Escondido Canyon gorge and beginning the home stretch.
As we neared the end of the hike the trail divided and we had to decide which way to go. As you can see, there was complete agreement.
On the home stretch; not far to go from here. Note that everyone is still smiling.
Approaching Vasquez Rocks and the parking area. Our goal is almost achieved.
At the end of the hike, Gene broke out refreshments to commemorate the finish of GeoTrek IV. Sparkling Cider for a toast, and honey roasted peanuts and cookies which had been won in the CGS raffle.
The party continues at the base of Vasquez Rocks. The day's hike was very successful, especially beautiful was the last part through Escondido gorge.
Vicki Pedone, Chair of the Geological Sciences Department, proposed a final toast to the success of GeoTrek IV, including increased participation by alumni, faculty, staff, and friends, and a new record in amount given to support Geology Student Scholarships.

Return to the GeoTrek IV index.
THIS PAGE LAST MODIFIED ON JULY 15, 2011
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geneandsuef@dslextreme.com

	Group photo at the start of the hike on the Pacific Crest Trail where it crosses Soledad Canyon. It was a beautiful day and we were eager to get on the trail.
	The hike started in the plutonic igneous rocks of the San Gabriel Mountains. Our authority on the subject was Doug Yule who provided us an overview of the important San Gabriel Mountains rocks.
	Soon after starting we had to cross the Santa Clara River. Luckily the river was only creek size and crossing was easy. In this photo, Lynn Sosa is followed across the creek by Syrus Parvizian.
	Here's Sue Fritsche crossing the boards that took us across one of the channels of the Santa Clara River.
	Tony Reid is followed by Doug Yule across the creek. No one fell in, so it was a successful crossing.
	Soon after crossing the Santa Clara River we came to the north bank of Soledad Canyon, location of the main railroad line between Los Angeles and the Antelope Valley. We stopped, looked, and listened before crossing.
	After climbing up the trail a ways, we came to a small outcrop where Gene stopped to talk about the rocks that were exposed.
	Trailcut exposure of soft, clayey weathered anorthosite. Anorthosite is made mostly of calcium-rich plagioclase feldspar which weathers rather rapidly to clay minerals when exposed to weathering elements on the earth's surface. Dating of unweathered samples of anorthosite from the San Gabriel Mountains shows that the anorthosite is 1.2 billion years old.
	Dike of weathered anorthosite intruding an older schist. The intruded schist in other parts of the San Gabriel Mountains is estimated to be around 1.7 billion years old.
	Dike of granite intruding the schist. The granite, if related to other granites in the San Gabriel Mountains, is most likely Mesozoic in age.
	Hiking along the Pacific Crest Trail just after crossing the Soledad Fault.
	A trailcut exposure of the Oligocene-Miocene Vasquez Formation is studied by the group. Gene gets them to describe the features that they see.
	Gene takes one of the many photos that make up this report. Go to next photo to see the result.
	Closeup view of an Oligocene-Miocene Vasquez Formation conglomerate. The angularity of the cobbles and boulders indicates a short distance of transport, and the reddish color is due to nonmarine deposition. The cobbles and boulders are made of anorthosite, gabbro, quartzite and other igneous and metamorphic rocks, some having come from the San Gabriel Mountains and others from farther away. The above features all point to deposition on a rather steep alluvial fan that existed here during the Oligocene and Miocene Epochs. A further conclusion is that the San Gabriel Mountains existed during the Oligocene and that they had already been eroded deeply into the plutonic igneous rocks.
	The flattened ridge crests seen in this photo, called stream terraces, are covered with a thin layer of river alluvium that was deposited in a broad river valley that existed here prior to uplift of the area and downcutting of the present stream valleys. The presence of stream terraces indicates that uplift of the area was sporadic, rather than continuous.
	The group continues up the Pacific Crest Trail to higher elevations. The San Gabriel Mountains are in the background.
	Yellow flowers like these were common along the trail.
	This large bush with purple flowers and fuzzy leaves is called Yerba Santa. The native Americans used it for a varity of medicinal purposes.
	This outcrop of an Oligocene-Miocene Vasquez Formation conglomerate shows the large size of some of the boulders. Boulders this large could only have been carried down the alluvial fan on which they were deposited by a debris-flow process.
	About four different colors of the Mariposa Lily were seen along the trail. This one, of course, is called a Yellow Mariposa Lily.
	California Golden Poppies, the California State Flower, had mostly finished their growing season, but there were a few left.
	Yucca plants were common along the trail, but only a few of them were blooming like this one.
	The light gray outcrops in this photo are exposures of igneous rocks that are surrounded by the Oligocene-Miocene Vasquez Formation. These igneous rocks are not mapped on Dibblee's map of the area.
	The group continues along the Pacific Crest Trail through the Oligocene-Miocene Vasquez Formation.
	Gene discusses the geologic history of the area, especially the history of the Vasquez Formation. In the background is a resistant outcrop of Vasquez Formation boulder conglomerate that was deposited in an alluvial fan environment.
	Gene uses his hands to describe the relationship between bedding in the Vasquez Formation and faults in the area.
	The group pauses for a break at the high point on the day's hike. It was mostly downhill from here on.
	Heading down into Escondido Canyon which we followed for most of the rest of the hike.
	In the center of the photo are exposures of brown, basaltic volcanic rocks that belong to a volcanic member of the Vasquez Formation. These rocks are underneath, hence slightly older, than the conglomerate deposits we had been hiking through previously.
	Outcrop of basalt from the volcanic member of the Vasquez Formation that was seen in the last photo. These rocks have been dated radiometrically and produce an age of about 24 million years, which is near the boundary between the Oligocene and the Miocene.
	Closeup of the basalt from the volcanic member of the Oligocene-Miocene Vasquez Formation. The blue-green patches are amygdules of an unknown mineral. An amygdule is a bubble hole that has been filled with minerals precipitated from groundwater.
	On the left side of the photo the group is hiking on conglomerate of the Vasquez Formation. On the right is an outcrop of basalt of the Vasquez Formation. Passing through the low spot between the two is the Agua Dulce Fault.
	We searched quite awhile for a shady spot for lunch and finally found a spot right on the trail where we could settle down in the shade for some nourishment.
	Sandwiches, veggies, fruit, cookies, and plenty of liquid were devoured by the group to make sure energy levels were high enough to get through the rest of the day.
	As the sun crept into our shady spot, we finished lunch and got ready for the afternoon hike.
	We stopped at this outcrop of the Oligocene-Miocene Vasquez Formation because it was a little different from the mostly conglomeratic deposits we had been seeing up to this point. See next photo.
	Pebble conglomerate and sandstone beds in the outcrop shown in the previous photo. The Vasquez Formation here is finer grained and better bedded than what we had seen up until this point. These layers were deposited in a river environment, as opposed to the alluvial fan environment of the earlier deposits.
	This Prickly Pear cactus with two bright red blossoms really brightened up the trail.
	Closeup view of a Prickly Pear blossom.
	Pacific Crest Trail tunnel under the Antelope Valley Freeway. It's a good thing that Escondido Creek was not full of water.
	Looking through the tunnel. It got rather dark in the middle, but by moving slowly and picking up our feet we made it through without incident.
	A short distance from the tunnel, Escondido Creek cuts a deep gorge through the Vasquez Formation. It was cool and shady here.
	Sue is smiling because there is only one mile to go.
	Resistant cliffs of the Oligocene-Miocene Vasquez Formation tower above the trail in Esondido Canyon.
	More Vasquez Formation cliffs along Escondido Canyon.
	The trail enters Vasquez County Park and descends into another gorge along Escondido Creek.
	We crossed Escondido Creek one more time before entering the final gorge through rocks of the Vasquez Formation.
	Excellent example of a debris flow deposit in the Vasquez Formation. The boulders and cobbles in the bed are scattered throughout the bed as would occur in a debris flow deposit, rather than being concentrated near the bottom of the bed as would occur if the bed had been deposited by traction currents in a river or turbidity current. The debris flow bed is about 40 feet thick and was deposited probably in a single day.
	Most of the beds in this exposure of the Vasquez Formation are river deposits. Although the thicker bed in the upper left with the pebbles scattered throughout is a small debris flow, the beds below it containing pebbles show that the pebbles are concentrated at the bottom of the bed. This feature is the result of waning traction current deposition by rivers.
	Exiting Escondido Canyon gorge and beginning the home stretch.
	As we neared the end of the hike the trail divided and we had to decide which way to go. As you can see, there was complete agreement.
	On the home stretch; not far to go from here. Note that everyone is still smiling.
	Approaching Vasquez Rocks and the parking area. Our goal is almost achieved.
	At the end of the hike, Gene broke out refreshments to commemorate the finish of GeoTrek IV. Sparkling Cider for a toast, and honey roasted peanuts and cookies which had been won in the CGS raffle.
	The party continues at the base of Vasquez Rocks. The day's hike was very successful, especially beautiful was the last part through Escondido gorge.
	Vicki Pedone, Chair of the Geological Sciences Department, proposed a final toast to the success of GeoTrek IV, including increased participation by alumni, faculty, staff, and friends, and a new record in amount given to support Geology Student Scholarships.