Earlier this week Western Science Center received a small collection of fossils recovered by Paleo Solutions from Bureau of Land Management property near Desert Center in eastern Riverside County. While the material was limited, some was identifiable, including a few unusual pieces.
This particular specimen is the first phalanx (toe bone) from what appears to be a bighorn sheep, Ovis canadensis, identified as such in Raum et al., 2014 (modern example below from a herd at Badlands National Park):
Historically bighorn sheep were widespread in the mountains and deserts of the American west, although their populations are now greatly reduced. There are still several hundred living in Joshua Tree National Park, not far from where this fossil was found.
Fossil bighorn sheep do not seem to be particularly common; this is the only one in the WSC collection (as far as we know). This specimen is most likely Pleistocene (rather than something more recent) because extinct Pleistocene animals such as Smilodon were found in the same deposit.
Reference: Raum, J., Aron, G. L., and Reynolds, R. E., 2014. Vertebrate fossils from Desert Center, Chuckwalla Valley, California. In R. E. Reynolds (Ed.), Not a Drop Left to Drink, California State University Desert Studies Center 2014 Desert Symposium: 68-70.