Blue Hole (Castalia)
The Blue Hole is a fresh water pond located in Castalia, Erie County, Ohio, in the United States. From the 1920s to 1990 the Blue Hole was a tourist site, attracting 165,000 visitors annually at the height of its popularity, partly because of its location on State Route 269, about southwest of the Cedar Point amusement park in Sandusky, Ohio.
Blue Hills (Washington)
The Blue Hills are perched on the north edge of the Seattle uplift, an east-west trending syncline or arch between the Seattle Fault and Tacoma fault formed by north-south compression of the bedrock. (See Puget Sound faults#Geological setting.)
Sharp downwarping of these formations has created numerous faults, including the dip-slip (vertical movement) Gold Creek fault that separates the two mountains. Strands of the Seattle fault, which east of here trend nearly due west-east, appear to turn to the southwest in the vicinity of Green Mountain.