These rocks that look a bit like limestone cave formations growing on a substrate of basalt (a rock not known for growing such things) are tufa (calcium carbonate) that were deposited with the help of algae, so said the sign at Picnic Cave, a short way down the ledge. It means cyanobacteria, blue-green algae. Tufa forms underwater. These were formed when Lake Lahontan covered over the area, likely when its height was controlled by overflow over Darwin Pass, which is about the same height.

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