Twenty million years ago, where you are standing was the bottom of a warm shallow sea. The Gulf of California covered the region.
Thriving in the warm waters were many varieties of fish, corals, and shellfish. Over thousands of years shells of oysters and pectens accumulated on the sea bottom and were covered with shofting sands. Thick deposits of shells formed reefs in the shallow sea. The Gulf retreated, faults shofted, and the land uplifted, leaving the ancient reefs high and dry.
The ridge to the south has a dark brown crust which is composed entirelyt of fossil mollusks. The reef is hard compated to the soft silts beneath it, and is more resistant to erosion. Can you see that erosion has weathered trhe softer sediment and brought them tight here to your feet. The buttresses beneath the ancient reef are known as Elephant Knees.
As you proceed up Fish Creek be on the lookout for signs of the fossil reef. It can be spotted in the overhanging cliffs above Loop Wash, just a few miles west of here.