Castle Rock was a 45 foot tall natural Sandstone formation located in, where else, but the township named for the feature. Settlers thought it had the appearance of medieval castle ruins.
It doesn’t look like the photo anymore, though. Time and erosion took their toll on the formation weakening it enough that a storm blew the top off of it after 1900.
The Society published a magazine on the history of Castle Rock in October 2004.