This image depicts cave systems and is excerpted from a larger map, that is part of Stan & Holly Deyos' Prudent Places USA(1) project. Click on the picture to see more details. Partial 6 states shown in this section are (from clockwise upper left): Idaho, Montana, Wyoming, Colorado, Utah and Nevada on the lower left.
1. http://standeyo.com/C2C_listeners/index.c2c.html