Portland Arch Nature Preserve is a 435-acre nature preserve near the Wabash River in Fountain County, Indiana and is a National Natural Landmark. The preserve encompasses the wooded valleys, ravines and rocky cliffs around the lowest section of Bear Creek, which flows northwest toward the Wabash River. Its name comes from the nearby town of Fountain, which was originally named Portland, and from a natural sandstone bridge carved by a small tributary of Bear Creek. Portland Arch Nature Preserve is managed by the Indiana Department of Natural Resources.
Portland Arch is one of only a few natural arches in Indiana. The arch was created through the Mansfield Sandstone by Bear Creek, undercutting the bluff on both sides. The sandstone was strong enough that it did not collapse. The Mansfield Sandstone is from the Pennsylvanian Period, some 230 million years ago. The cross stratification of the layers were formed in a shallow bottomed lake where it drops into deeper water. The slope reflects the change from the shallows into deeper water. Areas like this were used as rock shelters by Native Americans and early pioneers. Along the valley escarpment, talus rocks have fallen into the valley.
To get to the Preserve from Attica, travel south on U.S. 41 approximately 5 miles to C.R. 650 N. Turn right (west) on C.R. 650 N and travel roughly 5 miles to Fountain. Turn left on the gravel road and then left again on the next road to the north parking lot. The south parking lot and trailhead are further down the road, past the 90-degree turn.