The Trona Pinnacles are tufa towers that formed underwater during the Pleistocene, when the area was covered by a much larger and deeper Searles Lake. The tufa, a form of calcium carbonate, was precipitated by the action of algae where calcium-rich spring waters entered the increasingly alkaline lake. As Searles Lake shrank during drier Holocene time, the tufa towers have been exposed and subjected to erosion. The pinnacles are similar to the younger tufa towers at Mono Lake. Trona Pinnacles National Natural Landmark. Near Trona, San Bernardino Co., Calif.