Went with them twice already, one each on the upper and lower Kern River in July 2011. They are a professional outfit, which means that they'll require you to pass a swim test (in PFD - personal flotation device) before they allow you on the class V Thunder Run of the upper Kern. That was one of the best runs I've taken, almost all IV/V's. Don't worry, there are other runs on the Kern that are not as challenging for those who may be nervous. The scenery on the river was OK, but the experience was a blast. Highly recommended.
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