At the Great Salt Plains State Park about 10 miles away from Jet, you can dig for salt crystals at the salt plains. It's fascinating to dig up the crystals out just a foot or less below ground. (Call the Park office to check for availability, which is seasonal.) There is no fee for digging for crystals.
Tips: Bring sunscreen, good digging tools and your own supply of fresh water for drinking. It can get very hot. Sunlight reflects off the ground of the salt plains so be sure to apply sunscreen to the underside of the face and underarms also. Early morning the best time to go digging because it's cool.
A large umbrella is also extremely useful if you can anchor it down without it blowing away. It works wonders for a comfortable dig environment, and also helps you mark your own dig area when you have to go your parked car to get something.