Sandstone Peak – The top of the Santa Monica Mtns! EarthCache
Sandstone Peak – The top of the Santa Monica Mtns!
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Welcome to the Santa Monica Mountains National Recreation Area
EarthCaching Program. This earthcache site is available year round.
This cache is on trail. Please do not travel off trail for your
safety and preservation of resources.
Located at Circle X Ranch in the Santa Monica Mountains National
Recreation Area. Access to this cache is by way of trail from
either National Park Service land or State Park land. Mountain
bikes are not permitted for travel to this cache.
Information regarding Circle X Ranch and Sandstone Peak.
The two main trails to access this cache are the Mishe Mokwa Trail
and the Sandstone Peak Trail. There is free parking at either trail
head. Pets are permitted on a leash no longer than 6 feet (2
meters). Bicycles are not recommended on the trails at Circle X
Ranch. Horses are not permitted to this cache. Camping is
restricted to the Group Campground only. Permits are required for
camping.
• Circle X Ranch is open from sunrise to sunset daily.
• All plant material, rocks, animals, and historical features are
protected by law and may not be collected or disturbed.
Safety information:
• Poison Oak can be found in this area. It is identified by three
leaves ranging in color from green to crimson. The plant is
deciduous, so it does lose its leaves in the winter.
•Watch out for mountains lions, rattlesnakes and ticks.
Santa Monica Mountains National Recreation Area Visitor Center
Information:
Open daily from 9 AM – 5PM.
Address: 401 West Hillcrest Drive, Thousand Oaks, CA, 91360
Phone number: 805-370-2301
In emergency: dial 911
Geological information
This former Boy Scout Ranch is home to Sandstone Peak, the highest
point in the Santa Monica Mountains with an elevation of 3,111’
(948m). From here a view of Los Angeles, the Oxnard Plain, the
Valleys of Southern California, and the Channel Islands can be
seen. In 1948, the Boy Scouts acquired the land from a generous
donor and named the mountain in his honor. The scouts undoubtedly
scrambled up, over, and around this rusty colored ridge. Once the
National Park Service acquired Circle X, they changed the name back
to the previous name of Sandstone Peak which may seem strange since
it is not in fact “sandstone” and there is not any sandstone on the
Circle X site.
But why would it be referred to as Sandstone Peak in the first
place? It was not formed from ancient riverbeds or fossils or even
from sediments from far away. The rock that makes up Sandstone Peak
is igneous in origin. The word igneous is from the Latin word,
ignis, which means “from fire”. That means that Sandstone Peak was
created by a volcano!
First, let us picture what the area was like when Sandstone Peak
formed. Imagine yourself 24 million years ago. The dinosaurs are
long gone. There are no Santa Monica Mountains, just broad plains
that extend from the middle of California to the coast. In fact,
much of the land that makes up the Los Angeles area was underwater
at the time. Then a short period of time later, geologically
speaking, about nine million years, the volcanoes that created the
Santa Monica Mountains and the Channel Islands started to erupt,
however the lava only oozed underwater at first.
Yet about 15 million years ago the eruptions became explosive.
Volcanoes similar to the eruptions of the Cascades in Washington
and Oregon or the Andes in South America were a common occurrence.
For another 3 million years, the mountains continued to grow to
over 10,000 feet high. Three times taller than they are today!
Sandstone Peak is in the Conejo Volcanics Formation (16.1 to 13.1
million years old) and is composed of igneous rocks that include:
• dacitic breccias, andesitic breccias, basaltic breccias
• andesitic flows
• basaltic rocks
Look at the time scale below. About 24 million years ago the Lower
Topanga Formation (composed of marine sediment and non-marine
sediment) began to develop. There was an interruption in the
deposition of the Lower Topanga Formation, such that no geological
materials are preserved from this time. This is called an
unconformity. The end of the unconformity was marked by the
beginning of the Conejo Volcanics and Diabase Intrusions about16.6
million years ago. About 13 million years ago, the Conejo Volcanic
eruptions ceased allowing the Upper Topanga Formation to develop.
Although the Conejo Volcanics split the Topanaga Formations both
physically and in geological time, there is no sandstone at
Sandstone Peak!
Geological Time Scale
After 13 million years of erosion the amazing 10,000’ Sandstone
Peak is a mere 3111’. The remaining colorful, reddish rock is the
heart and core that gives us evidence for a process millions of
years in the making!
If you want to explore more about how the mountains formed, then
head down the trail to Inspiration Point EarthCache.
To log this EarthCache complete the following:
Sign your name in the register at the cache and put earthcache next
to it.
Click the link below to take the quiz and get your EarthCache
certificate:
Sandstone Peak Quiz
1. What type of rock is Sandstone Peak? Igneous, Metamorphic,
Sedimentary?
2. Look for the monument at Sandstone Peak. Who is the generous
donor the mountain was once named after?
3. Why do you think the peak was named Sandstone Peak?
Sources for this cache are:
Dibblee Jr., Thomas W., Ehrenspeck, Helmut E., 1990, Geologic Map
of the Point Mugu and Triunfo Pass Quadrangles, Ventura and Los
Angeles Counties, California, Dibblee Geological Foundation, Map
#DF-29
National Park Service, Santa Monica Mountains National Recreation
Area, Thousand Oaks, CA, 91360
Nicholson, Craig, Sorlien, Christopher C., Atwater, Tanya, Crowell,
John C., Luyendyk, Bruce P., 1994, Microplate capture, rotation of
the western Transverse Ranges, and initiation of the San Andreas
transform as a low-angle fault system, Journal of Geology, v. 22,
p. 491-495
Additional Hints
(Decrypt)
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