That is, the valley's rivers and glaciers cut down into the rocks more quickly where the valley now lie, than did other tributary streams and glaciers. Tributary drainages were left behind at higher elevations. These rivers and glaciers had more speed since they flowed down the western Sierran slope, which also provided them more erosive power to cut downward. Tributary streams flowing in from the north or south are relatively less steep since they flow across the western slope. In contrast, the tributary streams cut across these east-west joint systems thus gaining little advantage from them for eroding downward.
Rocks continue to flake off and the cliffs have receded significant distances since glacial times.
All major falls in the valley have created their own recessed alcoves in a way that glaciers could never have carved such alcoves. Both Yosemite's Upper and Lower Falls sit in such recessed alcoves. This time the joints are running horizontally. Two horizontal joint systems interrupt the vertical joint systems. One horizontal joint system is near the base of the upper fall and the other near the brink of the lower fall.