We’ve been back in Missouri for just over 5 years now, and in that time I’ve taken my mountain bike out to Howell Island Conservation area three times. Howell Island is located in the Chesterfield valley, off of N. Eatherton Rd, if you’re coming from the outlet malls you will head south/west towards Centaur road.
The area is pretty darn flat, though some of the trails are heavily rutted from vehicular traffic and flooding damage. I’m assuming the vehicular traffic is farming or park related, but not sure on that.
Howell Island is a really simple multi-use trailer, with 8 miles of trails. It is a very easy mountain bike ride, and not a highly trafficked route by any means, according to Strava only 9 people have ever completed the outer loop in the counter clockwise direction (which is always the route/direction I ride). The trail is a mix of fields and wooded areas.