#032 WVRd Series Traditional Cache
WVRdSeries: We are changing this to a challenge cache.
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Difficulty:
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Terrain:
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Size: 
(micro)
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The Williamson Valley Road Series is a Friends of Morgan Ranch Nature Park history project. Even numbered caches are on the E side of the Rd; odd on the W for 44 mi. WE RECOMMEND THAT YOU WORK 1 SIDE OF THE ROAD AT A TIME. Please pick up trash so the neighborhood trash-pickers are not drawn to the location.
SURFACE GEOLOGY AND ROCK OUTCROPPINGS ALONG WILLIAMSON VALLEY ROAD Granite Mountain dominates the skyline to the west of the southern end of Williamson Valley Road. The rock of which this mountain is composed crystallized deep in the earth nearly 2 billion years ago, being exposed by erosion more recently when this part of the North American plate rose in elevation; erosion became the dominant geologic process for millions of years. Exceedingly old crystalline igneous and metamorphic rocks form the backdrop for most of the landscape along the length of Williamson Valley Road. The shiny schist and phyllites exposed in the road cuts attracted early settlers to this area. Abundant and exceptionally well-preserved Native American petroglyphs are found in Inscription Canyon (not the development) just to the east of the road in a drainage which parallels the Crossroads off Williamson Valley Road. Further north, the Juniper Mountains, Santa Maria Mountains, and Big Black Mesa have been formed by uplift along normal faults at the base of each of these ridge lines. As a result of this uplift, the Great Unconformity - the erosional surface first described by John Wesley Powell in the Grand Canyon - is especially well-exposed along the southern edge of the Juniper Mountains, where it is much more accessible than in the Grand Canyon itself. Accompanying the faulting which allowed this great block of land to be uplifted was localized volcanism, which has left lava flow remnants lying, in some places, directly on rock which is more than a billion years older. As one heads north on Williamson Valley Road, the flat-lying Paleozoic-age sedimentary layers characteristic of the walls of the Grand Canyon underlie the road itself and can be seen in isolated hillsides both close and far. The younger volcanism, mentioned previously, allowed for heated iron-saturated water to create a zone of iron-oxide rich rock in one of the older limestones north of the Juniper Mountains, forming a very distinctive red zone just to the east of the road, which has been sporadically mined for hematite for the last hundred years or so. As one nears the north end of the road, the wide open spaces and distant views are characteristic of those of the Colorado Plateau of which this is the far southwestern-most edge. Picacho Butte forms the individual peak to the east of Williamson Valley Road at its northern end. The rock which comprises it is called dacite and was a highly silicic, viscous lava when it was erupted nearly 10 million years ago, forming a volcanic dome. This volcanism is believed to be some of the earliest activity associated with the San Francisco Volcanic Field, more conspicuous today around Flagstaff. Beth Boyd, Phd, Physical Sciences, Yavapai College The rocks in the outcrop at ground zero are the schists and phyllites of the Yavapai Group which Granite Mountain Pluton intruded into some 1.75 billion years ago. They are metamorphosed shales and volcanics from the volcanic arc that was at the edge of what was to become North America. The white rocks are quartz from late stage dikes associated with the intrusion of the Granite Mountain Granites as it was cooling miles below the surface.
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