For thousands of years Indians camped near the spring while on hunting forays. Their lodges dotted the prairie, and warriors stood sentry along the bluff watching for intruders. After the tribes moved on, deer and birds drank from the sulphur waters and bison wallowed in the mineral deposits. Although altered by man's hand, the Sulphur Spring remains a National Historic Landmark along the Lewis and Clark National Historic Trail. Two centuries ago, expedition hunters dipped their canteens there under orders from Captain Lewis for mineral water to treat an ailing Sacagawea.