Andrea Carter and the Trouble With Treasure — Susan K. Marlow

When innocent horseplay temporarily lands Andi and her friends in jail, they decide that a trip into the mountains will leave their troubles far behind. Accompanied by big brother Mitch and armed with a map showing old gold diggings, they can't wait to strike it rich. What could be better than two weeks of camping and horseback riding? But instead of gold they find heaps of trouble―trouble that leaves Mitch gravely wounded. Andi needs help fast. But who can she trust? And what good is a bag of gold when her beloved brother lies near death in the middle of nowhere?