Lost in the Wilderness by R. E. Toresen

Alicia can't wait until she goes on vacation! One morning at breakfast, Alicia's dad gets a phone call. It's some park ranger calling to ask her father to investigate some reports of "blue bears." Instantly, their vacation plans are canceled. Miserably, Alicia packs her bags and flies to the middle of the woods. She is dropped off at a lodge while her parents search for "blue bears."

There is a girl there named Suzanne who also rides horses like her. One day, as she is walking with her new friend, a girl slightly younger runs over. Instantly, she gives Alicia a cold shoulder as Suzanne introduces the girl as Lily. Lily is startled when Alicia is given Silas to ride.  He is the most dangerous horse on the farm. Fortunately, Alicia quickly befriends the horse.

The three ride into the woods and tie their horses to the trees and sit down. Suddenly, Lily exclaims, "I need to check Tofu's tether." After Lily returns, they return to the horses.  "Hey! Silas is gone!" Alicia hollers. Suzanne is horrified. They quickly go back and inform everyone of Silas's disappearance. Search parties go out. Miserably, the girls go to bed. The next day, Lily's horse Tofu is missing! Then, Suzanne's mom comes and tells them that Lily has gone, too. They realize that Lily has taken Tofu out on the trails to search for Silas!  They both hop on horses and hurry off to find them. Before long, Alicia hears a low rumble. Peering into the woods, she sees a mountain lion! What will they do?