On the Trail of Trouble — Carolyn Keene

Nancy, Bess, and George can hardly believe their eyes when they arrive at the Black Hills Buffalo Ranch. Aside from the awesome natural scenery, Mount Rushmore National Memorial -- with four larger-than-life US presidents -- towers nearby. But the girls have no time for sightseeing: They've come to help Bess's friend Kincaid Turner find out who stole a baby buffalo named Justice from her father's ranch.

At first, stealing a buffalo seems like a strange thing to do, but as Nancy and her friends investigate, they find a whole herd of suspects. Antoinette Francoeur, an eccentric animal rights activist, makes a habit of freeing caged creatures. Badger Brady, a rival buffalo rancher, has been making threats -- with an ax. And some archaeologists in the area aren't happy about the girls' snooping. Now it's Nancy's turn to round up the clues and stop a buffalo thief in his tracks.