The Upper Clear Creek River Run in Colorado is a challenging Class IV-V whitewater run that is best navigated by experienced rafters. The river features steep drops, tight and technical rapids, and several major obstacles such as "Nomad" and "Guide Ejector." The best time to float this section of water is during the spring runoff season, when flows range from 800-2,000 cfs. It is important to note that river conditions can change rapidly, and it is recommended to check the current flow levels before embarking on this run. Overall, the Upper Clear Creek River Run is a thrilling adventure for experienced rafters seeking a challenging and rewarding whitewater experience.