The Stolen Relic, Paperback

My friends and I knew before we got to Arches National Park that it's full of red cliffs arches, and rock formations -- plenty of places for hiking, biking, and getting lost. It's a good thing there are park rangers and guides to help tourist like us find our way. Or at east that's what we thought, until of the guilds left for a second to investigate some noise, and never came back.
It seems unlikely that a respected tour guide who knows the area like the back of her hand could just get lose. Something's fishy. And you can bet I'm going to get to the bottom of this before I find my way home.