The Tunnel Run section of the American River in California is a Class III-IV river run, with a total distance of 7.5 miles from Ralston Powerhouse to Greenwood. This section features a number of challenging rapids, including the infamous "Tunnel Chute" and "Chamberlin Falls." It is best to float this section in the spring months, when the snowmelt provides enough water flow to make the rapids more manageable. The recommended flow for this section is between 1,000 and 2,000 cfs. It is important for rafters and kayakers to be experienced and skilled in navigating Class III-IV rapids, as the Tunnel Run section can be dangerous for beginners.

Weather today, A chance of showers and thunderstorms before 1pm, then showers likely and possibly a thunderstorm between 1pm and 3pm, then a chance of showers and thunderstorms after 3pm. Partly sunny, with a high near 63. Light and variable wind becoming west northwest 5 to 8 mph in the morning. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.