Sonoma Volcanics’ Bedrock Earthcache EarthCache
Sonoma Volcanics’ Bedrock Earthcache
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As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org
There is a pulloff on the northbound side of the road directly across from the earthcache. All logging requirements can be done from the safety of this pullout! DO NOT cross the street, the traffic travels quickly around the blind curves!
This site is located on Hwy 29 on the western slope of Mt. St. Helena, about 3 miles from the RLS State Park. Mt. St. Helena is believed by many to be a volcanic cone. While it lies within the Sonoma volcanics zone, It is simply one of the last of a series of volcanic bursts along a seam/fault of volcanic activity during the period when the Sonoma volcanics area was active (this area stretches from west of Calistoga, over most of the northern and eastern part of Napa County). The eruptions likely began near the Petrified Forest, with the last of the blasts (more like a burble) forming Mt. St. Helena. Instead of forming distinct cones, there seems to have been a north-north west meandering portion of the fault system during this era, and as the fault slipped, spots opened in the crust, allowing hot gases and magma to leak through.
As a result of these many layers of magma, the strata are varied in color and rock composition. Some layers are high in iron content (stained red), and others have released rhyolitic glass, obsidian. Other layers are largely “landslide” in nature, where a weak magma release has largely acted as an agitator for the erosion of sedimentary soil landslides.
Logging Requirements:
Send the answers to #1-#3 to me through my geocaching profile.
1. List the name “GC2177C Sonoma Volcanics Earthcache” in the first line of your email. Also, list the number of people in your group.
2. Estimate the degree of tilt that these layers of sedimentary rock have made.
3. What colors do you see in these layers? Contrast with the colors present in the rocks at the TOP of the trail, near the Robert Louis Stevenson State Park signs (any roadcut on the top will do!)
4. (Per current gc.com guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). Post a picture of yourself and the Robert Louis Stevenson State Park signs OR your GPS and the roadcut explored to log these requirements.
Resources:
Trailside Geology of Northern California. 2006.
Additional Hints
(No hints available.)