Wasn't really birding this time I was taking pictures of the Kokanee Salmon spawning in the creek. Happened upon the Mergansers swimming in the creek. Thought they looked different from the Common Merganser that we see on the lake so often.
Since there is a bit of divergence of opinion, I'll add mine to the fray. I am solidly in the Mergus merganser camp for the reasons mentioned and illustrated by Jane. Probability wise, Common Merganser would be much more likely to be seen in the Sierras than Red-breasted, especially along a river. And in fact, according to this birdlist, Red-breasted is less than annual in that county. http://www.geocities.com/placerbird/PlacerCountyBirds.htm
Juvenile Common Merganser (Goosander). Note the whitish facial markings along with as others have said, white throat patch and sharp border between rufous and grey on the neck. Bill shape also favours Mergus merganser.