We visited Sand Prairie Conservation Area on July 23, 2018. The closest city is Benton in Scott County, Missouri. To get there take exit 80 off of Interstate 55 and turn left onto Highway 77. Travel 2 miles and turn left onto County Road 333. Travel about 2 miles to the area.
It is an interesting area, but nothing to drive a long distance to see, but worth seeing if you are in the area. It is a bit odd to see a huge area of sand and dunes no where near any ocean beach or lakeside. It even comes complete with desert plants such as wild cactus. The tall prairie grass and wild flowers were certainly unique in the desert-like savanna.
Scientists believe the sea (ocean) in prehistory times came all the way up this far into America. It was called the Western Interior Seaway. As you drive Highway 55, somewhere south past the Benton exit, it turns flat and sandy. I have heard that this evidence of the ocean beach front in Missouri. I have no idea if that is true, but there seems to be some bit of sense to it if you look at the geography, especially since it is also called "Swampeast Missouri." Another theory is that the sand deposits were associated with ancient channels of the Mississippi River and Ohio River.