CRATER OF DIAMONDS STATE PARK, Arkansas
Crater of Diamonds State Park, in Arkansas, is the only working diamond mine in North America where the public can search for real diamonds, and keep what they find. You can get rich, rich, rich.
Or, maybe not.
Statistics based on the number of visitors per year, the number of diamonds found, and the small size of the ones being found, suggest to me that this diamond mine has pretty much played out.
I visited Crater of Diamonds State Park about a dozen years ago, and I recently returned again. I noticed a few changes. The first time, there were a great many slivers of quartz sparkling in the sun, but this time everything shiny was gone. The first time, the ground was being plowed monthly, but this time the ground looked like it hadn’t been plowed in months, and some was rock hard. It was as if even the park personnel had given up. I also noticed that it’s not near as enjoyable when it’s 95 degrees, as when the weather is nice.
Don’t go when it’s hot, or cold, or rainy. Take your lunch, as you can’t get food there, but there are picnic tables both inside and outside the park.
They also have a 47 site RV campground, and a water-park, and three hiking trails.

I can see no reason I’ll ever go back to Crater of Diamonds State Park. The odds of finding anything just seem too unlikely. I think I would rather go a little north to Mt. Ida, and search for crystals. It’s also unlikely that you could find anything valuable searching for crystals, but at least you would most likely find something.
If you still want to dig for diamonds, just so you can say you did, do it the right way. The park allows each visitor to take home a 5 gallon bucket of sifted gravel (no soil). Just go in early, sift a bucketful of small gravel, and go someplace comfortable to carefully sort through it. Most of the diamonds being found are actually from the buckets taken home.