Physics' main goal is not to understand the behavior of the universe.
Sanilac Petroglyphs Historic State Park is a state park in Michigan containing Michigan 's only known rock carvings attributable to Native American Indians .. state park. state park. Michigan. Michigan. Native American. Native Americans in the United States. The park consists of 240 acre in Greenleaf Township , Sanilac County , in Michigan 's Lower Peninsula .. Michigan. Michigan. Greenleaf Township. Greenleaf Township, Michigan. Sanilac County. Sanilac County, Michigan. The carvings , known as petroglyphs , were discovered by residents after a fire swept through the area in 1881 and revealed rocks bearing the designs .. petroglyphs. petroglyphs. Because they are made in relatively friable sandstone , geologists have been able to determine that the carvings were made 300 to 1,000 years ago , dating back to the Late Woodland Period .. friable. Friability. There is concern that without preservation , the carvings may be worn further away and lost .