The "Hole in the Wall" area, in the middle of the Mojave National Preserve, contains photogenic tuff units, volcanic rocks that were formed, not by a flow of molten lava, but by the settling out of individual particles from a cloud of volcanic ash. If the particles are hot enough to stick together, the result is a "welded" tuff. That's what's happened here. The welding is uneven, so that the less cemented parts weather out more easily. One result is that the tuff weathers into spires and hoodoos and even more convoluted shapes. Another is "cavernous weathering," where the softer areas weather out to yield abundant hollows and caves, giving a "Swiss cheese" appearance to cliffs and slopes. The overall effect is otherworldly but attractive. It's possible these caves may have given the area its name, but if that were the case it should have been "holes" in the wall.…