The Mystery of the Vanishing Cave(1996)
(The fifth book in the Home School Detectives series)
A novel by John Bibee
Rebecca, Julie and Emily are at summer camp when they discover a hidden cave containing Native American artifacts and a skeleton. But when they bring people from the camp back to the site of the cave the next day, there is no sign of the cave at all. Kids 8-12 can join in on the adventures as the Home School Detectives sort out false leads and follow the real trail to an exciting conclusion in this fifth book of the series.
Used availability for John Bibee's The Mystery of the Vanishing Cave
August 1996 : USA Paperback