I spent part of Sunday at Hot Springs State Park in Thermopolis, Wyoming. This site is billed as having “The World’s Largest Mineral Hot Spring” (see photograph). The springs, which feed three bathhouses/pools in the park, were acquired from the Shoshone and Arapaho in a 1896 treaty with the stipulation that they be maintained free of charge for everyone. So far, that stipulation has been honored. I didn’t have time to visit any of the bathhouses—and hadn’t brought a swimming suit, not having read up on Thermopolis before I left Loveland. But that was okay; the previous day’s drive had been hot in advance of a front (87 degrees west of Casper in late September!), and I was relishing the refreshing coolness on Sunday. I was also relishing the lack of crowds while I had the chance; things would be very different at Yellowstone.

The park has several places to see the travertine formations created by runoff from the springs. The travertine is deeply “stained” by heat-loving bacteria, making a colorful sight. One of the most interesting things about the hot springs area is the profuse growth of cyanobacteria (blue-green algae) in the runoff. These bacteria form long, thick mats that ripple in the current like hair. The water where they grow is about 110 degrees Fahrenheit. Reddish and orange bacterial mats predominate where the water is warmer.

The park is on the Bighorn River, which is actually the downstream reaches of the Wind River. The dual names resulted from the fact that, until Wind River Canyon was discovered, no one realized that the Wind River cuts north through the Owl Creek Mountains. Just south of Thermopolis, it becomes the Bighorn. The original Crow (Apsáalooke) word for the Bighorn is a whopper: lisaxpúatahcheeaashisee, “which translates to English as Large Bighorn Sheep River” (thanks, Wikipedia).

Besides the hot springs, the park also features a suspension bridge over the Bighorn River and a drive through a hilly range that’s home to a buffalo herd. The red sandstone hills surrounding Thermopolis date back to the early Triassic and are called the Red Peak Formation (part of the larger Chugwater Formation). According to a park sign, the nearly 600-foot-thick formation is almost devoid of fossils because one of the planet’s great extinction events had taken place at the beginning of the Triassic.

I spoke to a man who was using a decoy dummy to train two 8-week-old pups to retrieve ducks. They were splashing in a little inlet of the Bighorn River where there was runoff from a large hot spring. The water temperature at that location stays in the 70s year-round, he said. The pups were having a blast but were more interested in playing and checking out visitors than retrieving the dummy. They were joyful, muddy, and very, very wet.

Next up: A visit to the Wyoming Dinosaur Center.