Three different rock formations were seen during the Day 4 hike. The oldest was a pink-colored sedimentary rock unit called the Sespe Formation. It originated as river deposits beginning about 40,000,000 years ago and is seen in the bottom half of this picture taken of the western slope of Hondo Canyon. On top of the Sespe Formation is the brown to gray sedimentary rock unit seen in the top half of the picture. It is called the Lower Topanga Formation and was deposited in shallow ocean water beginning about 25,000,000 years ago.