Located near Portland, Missouri, Research Cave is a Native American archaeological site declared as a National Historic Landmark in 1964. It is similar to Graham Cave in numerous aspects. It also contains deposits that show evidence of intermittent occupation over the last 8000 years.
Sadly, the Research Cave was not looked after in the best manner possible. It has been looted a good number of time in the past, possibly damaging its integrity. This is the main reason why its National Historic Landmark title is being questioned and disputed today.
Current, yet unidentified, owners of the Research Cave property have now set up measures to prevent further unauthorized visits and looting. Further details about it are still to be determined whether it will be open to the public again.