The Legend of Red Horse Cavern — Gary Paulsen

Will veered to the left and ducked into one of the passages leading away from the palace room. Sarah stumbled and fell. Will pulled her up. They could hear the big man closing in on them. Will took another left turn and then another. Scarface's footsteps echoed in their ears.
 
Deep in the damp, dark caverns of the Sacramento Mountains, Will Little Bear Tucker and his friend Sarah Thompson discover the secret of an ancient Apache legend. But armed bandits are after them. A headless Indian brave haunts them. And when they lose their way, they may not escape the eerie underground maze alive.