Marble Quarry is a hiker-biker campsite located at mile 38.

2 of the C&O Canal in Montgomery County, Maryland, offering free first-come, first-served camping with a chemical toilet, picnic table, fire ring, and hand pump water (non-potable; water available mid-April to mid-November).

The site accommodates up to 5-10 tents and is situated 1-5 miles from the nearest parking area, making it accessible for paddlers and hikers exploring the Potomac River corridor.