Rio Grande Turtle & Tortoise Club

I found a turtle. how can i tell if it's wild or a lost/abandoned pet?

First, where did you find it? If you come across an aquatic turtle in the Bosque, it is probably native. If, however, you find any turtle wandering in the Foothills, a Wal-Mart parking lot, out on the West Mesa, or way up in Taos, it's a pretty safe guess that it doesn't belong there. There are ten species of turtles that are considered native to New Mexico, of which only two - the western box turtle (with two subspecies, the desert box turtle/Terrapene ornata luteola and the ornate box turtle/Terrapene ornata ornata) and the red-eared slider (Trachemys scripta elegans) - are commonly kept as pets. Red-eared sliders, which appear to be native to limited areas of the Pecos and Canadian River drainage,  have become established in the Rio Grande and elsewhere from people illegally releasing their pets. The NM Wildlife article, “Turtle Trouble," includes an excellent color guide to the turtle species of New Mexico. If in doubt, contact the RGTTC or the NM Department of Game and Fish for advice.