The Edward “Ted” and Pat Jones Confluence Point State Park is just a short drive from St. Louis and just across the Mississippi River from Alton, Illinois. You do have to drive about 4 miles down a rock road in order to get to the parking lot.
Since this area is prone to flooding, activities are limited to day-use only. It is also a good idea to call ahead in order to make sure the park is open. From the parking lot there is a short trail that follows the Missouri River to the confluence with the Mighty Mississippi.
We have had a very rainy summer so while we were there, the river levels were high so part of the trail was flooded, but you could still get a good view of the rivers emerging into one.
There is a not a lot of activities at this park besides the short trail, so we also drove across the Clark Bridge to Alton, Illinois. We stopped at the Melvin Price Lock and Dam Museum. There was a lot of information exhibits and they even give tours of the dam daily. My favorite part of the museum was the waterfall/river exhibit outside. Alton also has a lot of other neat activities and just a short drive along the river road is Grafton, Illinois.
You can get more information from the Missouri State Parks website.