Over an eight-mile stretch of the Colorado River downstream from Kremmling, boaters navigate a roller coaster of seven raging rapids rated Class IV+ or V. Timberline Tours, which started guiding Gore Canyon in the mid-seventies and remains one of three companies permitted to run it (and the only one based in Eagle County), requires guests to be over 18 and in good physical condition. After a two-mile flatwater warmup paddle, everyone on the boat must demonstrate an ability to swim under the raft and then get back in unassisted while shooting a Class III rapid before proceeding to the main event. “Traditionally our Gore Canyon season starts around mid August and runs to the end of September,” says Greg Kelchner, who founded Timberline Tours in 1971 and still runs the business at age 76. The guides who run Gore Canyon, says Kelchner, “are the cream of our crop.” ($2,200/private boat of eight)