Great roadside boulder.
North side of the road, between Cedar Grove and Road's End. I will update this when I can get more exact directions.
The Mars boulder is 4.0 miles east of Cedar Grove and 1.4 miles west of Roads End. It is easily seen from the road. Park in a small dirt turnout on the south side of Hwy. 180, then cross north over the road and walk a short distance west.