Research Cave is a Native American archeological site near Portland, Missouri. Locally known as "Arnold-Research Cave" or "Saltpetre Cave", the cave is located in an outcrop of sandstone approximately 2 miles (3.2 km) north of Portland.[3]:2 it was occupied intermittently for over 8,000 years. It has been recommended for de-designation as a National Historic Landmark due to looting.[2]