The oldest rocks along this leg of the hike are two different intrusive, plutonic igneous rocks: a light-colored granodiorite on the left side of this photo and a dark-colored quartz diorite on the right side of the photo. You can see in this photo that the contact between the two rock types is abrupt and that in the upper right corner is a granodiorite dike in the quartz diorite. These observations show that there were two separate intrusions of different composition and that the quartz diorite is the oldest (it had to be there first in order to be intruded by the granodiorite dike). The granodiorite has been dated at about 102,000,000 years old.
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