Biking the Great River Road May, 2006 We went to Illinois again in May. We camped at Pere Marquette State Park, and on Saturday we biked from the Piasa Bird in Alton back to the park. It was at least 20 miles. The trail is on the shoulder of the road for part of the way, but more of it is its own separate path. The weather was perfect, and the park was a real good one.