"These are lodgepole pines that died by shifting hot spring run-off. By capillary action the trees soaked up mineral laden water, which colors their bases white and retards decay. Dissolved minerals in the water deposited a crust of white silica on the bottom of the dead trees and stumps. This silica, a non-crystalline compound, slowly impregnates the wood and over time, with the absence of oxygen, could eventually petrify the wood. These skeletons have stood here for decades."
From Yellowstone National Park Sept 2016