If you like geodes, check out Rockhound State Park in southern New Mexico -- They let you take out 20 pounds of rocks per stay (or day?). Scenic hiking area surrounds park where you can search for rocks. Also, check out the old timers just outside the entrance (watch for several racks of solar panels), where you can buy geodes by the pound, or pick out special cut and polished specimens from their collection. Deming also has a little mining museum.
Nice little visitors center hosts local youth groups one weekend near the Holidays (caroling, hot chocolate, homemade cookies, etc.), and the whole town shows up. The scouts light luminarias along-side the road for a couple of hundred yards up to the entrance.
Some sites have electric and water, but none have sewer; although dump station is near entrance. Some sites have covered picnic tables for shade, but it gets hot in the summer. Best time to visit is in the cooler months.
Kids love this place, which also has a nice playground.
It's about 15 miles off I-10, southeast of Deming, NM. Great little state park.