The hole in the seashell looks man-made. The natural holes in seashells are usually a perfect drill hole from a rival crustacean, such as a horse conch, with no breakage around the hole. It's difficult to say what made it, but the shell is a typical and common type of salt water cockle shell. Since New Mexico doesn't have a coast, the shell was obviously imported. It doesn't have the look of extremely old shells, where most of the patina has worn away, nor the polished perfection of a shell that has tumbled for years in the ocean. The edges of the hole are ragged and broken, which suggests drilling or puncturing.
I have found many gorget-type shells that were obviously drilled, and plenty of others in which the holes were completely smooth. The bottom line is that it's hard to tell, but the location being far from the ocean makes me suspect that it could be man made.
