Tears of the Turtle Cave, in western Montana’s Bob Marshall Wilderness, is the deepest known limestone cave in the United States. Formed in Cambrian Pagoda Limestone within a karst landscape, it is a cold, muddy, mostly vertical vadose solution cave with narrow fissure passages and about 50 short rope drops rather than broad chambers. Since its entrance was found in 2006, repeated expeditions have steadily extended its surveyed depth, especially after the first multi-day trip in 2014 established its national distinction. By August 2024, exploration had reached 2,477 feet deep and 1.88 miles long, ending at a sump while suggesting the system may continue farther.