David,
Shipwreck may give you other ideas but if you magnify the following route that I use below, you will notice Machens is only 3 miles from Portage Des Sioux, which has an old small town marina where we park before riding into St. Louis to catch the Amtrak. There is nothing at Machens other than the trailhead, that's it. You will notice on the map that you can cross the Mississippi on route 67 into Alton, IL or if you travel further south along this route on the St. Louis River trail, about mile 21.5 you will see the old Chain of Rock Bridge, which if open is an excellent way to cross over and onto the IL system of bike trails. Highway 67 into Alton can be really busy so try not to cross during rush hour. Yes it has a shoulder but it can be littered with stuff to eat your tires. The Mckinley bridge is another opportunity to cross over into IL and here St. Louis Jerry can give you more information, a nice fellow on this board who is always willing to share information.

https://ridewithgps.com/routes/12321040