This is Little Crazy Horse Canyon very close to Goblin Valley State Park. This, along with the park, is one of my absolute favorite places in Utah, and when not flooded is a very easy and safe hike.
In order to not contribute to some idiot killing themselves I would like to make very clear, this canyon was flooded not flooding. If there is any risk of rain, please please, please, do not go into a slot canyon. A cool experience is not worth dying for. (Though it would be a cool way to die...)