Sigurd Olson's nine books were published between 1956 and 1982. For those who haven't read him, Douglas Wood and Alanna Dore of the Listening Point Foundation recommend his first, "The Singing Wilderness." His son Bob's favorite is "Runes of the North." For more information on Sig Olson, see www4.uwm.edu/letsci/research/sigurd_olson/contents.htm.
For more information on the Listening Point Foundation, see listeningpointfoundation.org.