Also, during this time, the slopes and cliffs of Yosemite Valley were subject to slow retreat due to mass wasting, which was governed by the spacing and pattern of joint planes. The rate of rockfall generally was too slow to produce talus slopes. All of the falls in Yosemite Valley proper should have achieved their full heights by the time the climate changed profoundly 33 million years ago. Overall the climate became cooler and drier, and rates of chemical weathering de creased substantially. Resistant summits such as El Capitan, Middle Cathedral Rock, Sentinel Dome, North Dome, Half Dome, and Mt. Starr King stood only about 10 to 30 feet higher than today's summits.
Similar reconstructions apply to other similar faces.
The forbidding, exfoliating northwest face of Half Dome, instead of being slightly concave, would have been slightly convex, much like its back side. Royal Arches was an ordinary cliff, some what like its western continuation, neither hav ing significant arches. Over the 32 million years that had elapsed since the start of the Cenozoic era, the Merced River had cut down through resistant bedrock to perhaps about 3800 feet elevation just west of Yosemite Valley. In the Valley the river meandered across a flat floor, at perhaps 3850 to 3900 feet elevation, so the Valley was slightly deeper than today's, and slightly nar rower. In modern tropical lands, subsurface weathering can extend 2000 feet down through bedrock, and beneath the Merced River such weathering may have locally extended to this depth by this time.