When I was telling my mom about my trip to Lost Valley, she says we visited a nearby theme park called Dogpatch USA when I was growing up. It was located just south of Harrison on Ark. 7. Had rides and lots of downhome characters. The park closed in 1993.
You can still visit the cave, now called Mystic Caverns.
http://en.wikipedia.org/wiki/Dogpatch_USA