It was 100 degrees on the July day I was here. The grasslands aren't very grassy...more like scrub and near desert. So you have to really want to visit. South of La Junta there's one area called Iron Spring where you can see Santa Fe Trail ruts...but watch out for rattlers as you walk into the desert a short distance. Vogel Canyon, also south of La Junta, is also interesting. I only did the fairly short rim trail, but there are nice views of a small canyon that is important historically and geologically; there's also a longer trail up through the canyon. There are other hiking opportunities, as well. Most people will be surprised to find this kind of climate and landforms in Colorado.
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