The earliest report of bone material found within the lava tubes at Craters of the Moon dates back to the 1880s. A variety of bovine-like bones were collected from the lava tubes, but are too poorly preserved for definitive identification. Packrat middens within the lava tubes contain bone material including the remains of rodents. Bighorn sheep, bison and grizzly bear bones discovered in lava tubes prove that these large mammals once roamed the area.
Numerous tree mold impressions are preserved in the basaltic lava flows. These impressions were formed as lava flowed around a fallen or standing tree. The molds display the impressions of charred wood. Moisture in the wood may have prevented incineration of the trees and charcoal found in these areas has been utilized for carbon dating of the flows. One of the best places to view these features is on the Tree Molds Trail.