Big Rock is a primitive fishing access site on the Boulder River near Big Timber with approximately 5 campsites, a hand launch boat ramp, and vault toilet facilities.

The site offers direct river access for fishing and swimming, with some shaded sites positioned right on the riverbank; camping is free with a 7-day limit and pack-in/pack-out requirements. Access is via a well-maintained gravel road about 3.

5 miles south of Big Timber off I-90 Exit 470.