We had only had one night at Bottomless Lake State Park, so we just took an hour to explore the Park. It is really a chain of eight lakes that are actually sinkholes that range from 17 to 90 feet deep. They were formed when circulating water dissolved salt and gypsum deposits to form subterranean caverns (just like Carlsbad). Eventually, the roofs of the caverns collapsed from their own weight. Sinkholes resulted & soon filled with water & formed the existing lakes. You can only swim in the big lake, but the rest are open for trout fishing in the winter.