This contact between two rock formations on Camelback Mountain
represents over 1 billion years of "missing time"! In geology, such a
contact between rocks is called an unconformity.
Notice the dividing line running from near the center of this photo to the
lower left corner. Rock ( / , above that line is the
age (approximately 30 million years old) Camel's Head Formation. Below that line is
(~1.7 billion year old) , which forms the slope below the
vertical Tertiary rock face.
This feature can be seen in many places on Camelback Mountain -- this picture
was taken just off of the Echo Canyon Trail to the summit. In the
background of this northeast-looking view are the McDowell
You can read more about these rocks in my FREE, short
GeoStory, called "Missing Time" (< 1 MB, download as a PDF).