Rockshelter and spring at Arcola Mills, north of Stillwater, in Washington County.  Local historian Don Empson stands to the left of the spring exit.  Large springs were choice sites for mills because springs do not freeze over in winter, and because the flow of water from springs varies much less than that of surface streams.  While the spring at Mooers Lake is the largest in Washington County, the spring at Arcola Mills is also quite large.