The "narrows" in Lost Burro Gap.  Here can be observed one of the most fossiliferous geologic contacts in all of the Death Valley district--the contact between the Lower to Upper Devonian Lost Burro Formation, seen here as the pale gray banded bedding along the lower slopes, and the overlying Lower Mississippian Tin Mountain Limestone, which is the dark blue, thin to massively bedded material from just above center to the top of the ridge line. Common to abundant silicified brachiopods, including the striking, attractive species Eleutherokomma can be observed in situ here in a ten foot-thick limestone interval just below the contact with the overlying Tin Mountain Limestone; indeterminate crinoid debris and lattice-style bryozoans can also be seen along those same carbonate bedding planes. Lower in the Lost Burro, in strata older in geologic age, many beds are comprised almost entirely of hemispherical and "spaghetti" type stromatoporoids--ancient species of sponges all tangled together in their original life positions.  Near Trail Canyon, south of Furnace Creek Ranch along the eastern side of the Panamint Range, scientists have recently discovered several species of both jawed and jawless fish from the Lower Devonian section of the Lost Burro Formation.

The overlying Lower Mississippian Tin Mountain Limestone may be one of the most fossiliferous units in all the Great Basin. Numerous species of invertebrate animals have been identified from it, including 14 species of corals, three varieties of bryozoans, 18 species of brachiopods, two kinds of pelecypods, 15 species of gastropods, two cephalopods (a goniatite and a nautiloid), a trilobite and a worm.