The history of this giant grinning glob of granite is more "gag" than "gruesome." The boulder was originally painted sometime around 1900 by a work gang on the Santa Fe Railroad line, to emphasize its natural resemblance to a human skull. For years, the train conductor would tell the passengers a tall tale of a scout who had been killed by Indians, and that his skull could still be seen "just as the Indians went off and left him way back in 1860." Just at that point in the story, the train came around a bend, and there was the huge skull rock!
Directions: The town of Congress is 16 miles northwest of Wickenburg, Arizona via Highways 93 and 89. From the intersection of Highways 89 and 71 in "downtown" Congress, continue about 2 miles northeast on Highway 89 and turn left on the signed road to Hillside. After about 6 miles on this graded dirt road (1 mile past the railroad siding of Piedmont), the skull rock can be seen to the right (northeast), several hundred feet beyond the railroad tracks. The rock is behind a barbed wire fence, but is clearly visible from several vantage points along the road.
Last visited: January 2019.
Standard disclaimer: Sites are described for entertainment purposes only, as they were at the time of my last visit. I can not vouch for the current condition of the site or its accessibility.