The Upper South Boulder Creek river run in Colorado is a challenging Class V section of water that is best suited for experienced kayakers and rafters. The river features numerous technical rapids, including tight drops, boulder gardens, and steep chutes that require precise navigation. The best time to float this section of water is during the spring runoff season between May and June, when water levels are at their highest. At these times, flows can range from 300 to 800 cfs, providing plenty of excitement for adventurous paddlers. However, it is important to note that this section of river should only be attempted by experienced boaters with the appropriate gear and safety equipment, as the risk of injury is high.