Note that due to the preferences of the New York Heritage Digital Collections, all materials sourced from their database will be in the following order: Digital Collection, Holding Institution, Title, NYHDC, access date.
Bierhorst, John, and Olive Natural Heritage Society. The Ashokan Catskills: A Natural History. Fleischmanns, N.Y.: Purple Mountain Press ; Arkville, 1995.
Diamond, Joseph E. “The Archaeology of Bear Trap Spring Rockshelter, Ulster County, New York.” North American Archaeologist 34, no. 2 (2013): 169–201. https://doi.org/10.2190/NA.34.2.c.
Meshejian, Haig C. “CATSKILLIANA.” Onteora Record, July 21, 1960. Hudson River Valley Heritage Historical Newspapers. https://news.hrvh.org/veridian/?a=d&d=jaaggddf19600721-01.2.31&e=-------en-20--1--txt-txIN-------#.
Sickler, Vera Van Steenburgh. History of the Town of Olive: 1823-1973. Olive[?], New York, 1973.
Stradling, David. Making Mountains : New York City and the Catskills. Weyerhaeuser Environmental Books. Seattle: University of Washington Press, 2007. https://research.ebsco.com/linkprocessor/plink?id=24718124-2bc5-327f-b334-1c799520094e.
"[...] were formed through erosion from glaciers over hundreds of thousands of years during the ice age over 10,000 years ago." — Bierhorst.