Goodwin Canyon was offered as a replacement whitewater run for the Camp 9 run on the Stanislaus after it was dammed. It is by no means the same family-friendly run that the Camp 9 run was, as it is a Class V run for expert boaters only. It has a fairly dependable dam release and can be done quickly, so two runs in a day is common.
This section of river has three interesting Class IV - V rapids with a scattering of Class III rapids in between. The first big rapid is Mr. Toad's Wild Ride which is a powerful series of waves that end up slamming into a wall on the bottom right. The left side is full of sieves so please be careful over there. The next big rapid is Matterhorn which is an 8 or so foot drop with no easy landing. Most people portage this one on the right.
The final big one is Haunted House, which is and exciting hole that likes to flip boats at all levels. This wouldn't be a big deal, but the swim here can sometimes be unpleasant. Many a raft has flipped here and this rapid has been swum by many with varied levels of joy.
In general, this is a fun run with some dangerous places on it. Please be especially careful of the left side of Mr. Toads and Air Matress (which is the last rapid).
