The western Petit Jean Mtn. is the high point of Yell County. I have a cache at the high point named (of course) "Yell County Highpoint" (GCKZ8X). When I placed the cache, I measured an elevation of 2434 feet with my Garmin eTrex Vista.
The eastern Petit Jean Mtn. is the high point of Conway County. Its high point is at an elevation of 1207 feet (according to the following web location: http://www.cohp.org/ar/arkansas.html, which is the Arkansas page for the County Highpointers Association.)
Having visited both, I can assure you that the eastern one is more scenic and is one of my top two favorite places in Arkansas (the other being the Buffalo River). -- ORR
"Wildness is a necessity." -- John Muir
"When you go to hide a geocache, think of the reason you are bringing people to that spot. If the only reason is for the geocache, then find a better spot." – briansnat