Erratic Rock State Natural Site is a state park in the Willamette Valley of Oregon, United States. Featuring a 40-short-ton (36 t) glacial erratic from the Missoula floods, the small park sits atop a foothill of the Northern Oregon Coast Range in Yamhill County between Sheridan and McMinnville off Oregon Route 18. The day use only park is owned and maintained by the Oregon Parks and Recreation Department.