Outdoor Girls of Deepdale by Laura Lee Hope

The Outdoor Girls of Deepdale was the first book in a long-running series centering around four girls: Betty Nelson, Mollie Billette, Amy Stonington, and Grace Ford. The girls go on many exciting adventures and solve mysteries. In this book the girls go on a long walking tour and in the process find a hundred dollar bill. Who owns the money and why is such a mysterious note attached? (Introduction by Elizabeth Wilcox)