House Mountain, Sedona, Arizona | A final determination for how the Miocene House Mountain shield volcano was emplaced could only be determined by visiting an outcrop where the lava and red bedrock were in contact. After 15 million years of erosion, most contacts were obscured by soil and vegetation. However this small outcrop revealed no slickensides (evidence for faulting) but rather an eroded surface that was covered by gray scoria erupted in the cinder cone phase (right).
This scoria buried a bedrock slope (left) where the mechanical pencil lays on it. Thus, the answer to why House Mountain lava did not flow north into the modern valley is that this area was the site of a bedrock high that precluded lava from flowing in that direction. The red bedrock was subsequently eroded away leaving House Mountain volcano with flows on only three sides. (Photo and text by Wayne Ranney)
Holm, R.F., and Wittke, J.H., 1996, Geologic Map of the Summit Area of House Mountain, Yavapai County, Arizona: Arizona Geological Survey Contributed Map CM-96-C, map scale 1:6,000, 26 p. and 2 map sheets. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1102
Holm, R.F., 2016, The North Verde Volcanic Field, Verde Valley, Arizona.. Arizona Geological Survey Contributed Report, CR-16-E, 31 p. and 6 appendices. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1687
Bezy, J.V., 2012, A Guide to the Geology of the Sedona & Oak Creek Canyon area, Arizona. Arizona Geological Survey Down-to-Earth DTE #20, 42 p. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1694