US 101 Franciscan Cut Earthcache
Size:  (not chosen)
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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.
This cache is available from within your parked car, and thus VERY Handicap accessible.
Intro: North of Leggett and South of Richardson Grove State Park is a winding section of US 101 that winds dramatically along sheer cliffs and the rivers and creeks that form steep drop offs. You can ONLY access this cache SAFELY from the northbound lanes. It is a wide and visible shoulder beneath towering bluffs.
Send the answers to #1-#4 to me through my geocaching profile. DO NOT post the answers to any logging requirements on this site.
1.List the name “GC2D1F5 US-101 Franciscan Cut Earthcache” in the first line of your email. Also, list the number of people in your group.
2.Based on your reading and observation, Are these rocks sedimentary or igneous in origin? Are they sharply tilted and crumpled or simply gently tilted? Why?
3.There are several wide veins of an apparently denser rock than the majority of rock visible in this cut. How wide is this vein? Is it lighter or darker than the other base rock?
4.What do you think caused the massive landslide you see here? Man (making the road) or nature (weather and area quakes etc.) Why?
5. Optional: Post a picture of yourself and/or your GPS with your log that shows the highway rather than the eroded cliff. DO NOT show any of the pertinent views that might make “armchair earthcaching” possible for those that don't play by the rules!
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
The highway in this area follows the deep and winding canyon of the South Fork of the eel River along most of its route between Leggett and Rio Dell. Large outcrops of rock make steep bluffs. Occasional small outcrops, high on the hillsides, mark old landslide scars, where the bedrock was exposed as the soil slid off the slope.
Franciscan rocks lie beneath most of the area. Rocks in the Eel River basin (the river bottom in this area and the alluvium area near Ferndale and Humbolt Bay to the north), are soft sedimentary formations deposited during Tertiary time (after the Cretaceous time ended). These Franciscan rocks are much younger than the Franciscan rocks found farther inland. As a result they appear much more “sorted” into layers and much less jumbled than those we see in the Bay area and further inland. Basically, that is because there were the last rocks jammed into the trench. Roadcuts and deeply eroded areas throughout this region show sedimentary LAYERS that are often gently tilted, rather than tightly crumpled and broken. Since they were the last ones shoved into the trench there was not as much pressure, AND they were the first ones to rise out of the trench into the cliffs you see before you!
Other Information: This area that you're driving is the NEW and WIDE version of Hwy 101. The old version was called “The Slab” and was a skinny and twisted part of the highway that caused seasoned truckers to shudder. There are a couple of caches on this now gated and abandoned “slab” of interstate...but that's another hunt.
Landslides often happen in this area for a variety of reasons:
1)Human interaction – new roads, new buildings, etc. remove trees and grass and other natural items that were “holding the soil together.
2)Natural – earthquakes, floods, river/stream erosion, freezing/thawing and many other natural causes cause these cliffs to tumble into the rivers below.
Alt & Hyndman, Roadside Geology of Northern andCentral California. Mountain Press Publishing. Missoula: Montana. 2000.
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