Tom Derringer and the Steam-Powered Saurians. The Adventures of Tom Derringer, #3

In 1884 the "Bone Wars" between rival paleontologists were in full swing, driving fossil hunters to outrageous lengths in pursuit of the latest finds, when reports came out of the Wasatch Mountains in the Utah Territory of the most amazing discovery yet. An adventurer went into the mountains to investigate - and he didn't come back. Fresh from his adventures in the tunnels under Los Angeles, Tom Derringer is hired to find the missing man.
With his assistant Betsy Vanderhart he sets out into the wilderness, where he finds more than he bargained for...