K.H. Koehler 
DINOSAUR VALLEY [EPUB ebook] 
The Archaeologists #1

Cowboys vs. Dinosaurs!

Lady Anna Rutherford, scholar and intrepid archaeologist, has crossed the Atlantic to launch an expedition into the Sonora Desert to find her missing twin brother, Edmond. But the unforgiving Sonora is only the beginning of their troubles, because soon enough, the search party encounters an ancient, forgotten valley full of primeval creatures with the power to rend men in half.

Before long, their hunt for Edmond becomes a tooth-and-nail fight for survival when the ancient, man-eating creatures of this forgotten land begin hunting them. It will take their combined knowledge, courage, and survival skills if they are ever to escape Dinosaur Valley.