Identification: What are these mushrooms?

I found these by the river in northern California in the midst of cottonwood trees. Can anyone positively identify them?

 

Looks like a common Fly agaric (Amanita muscaria), but could also be some other member of the genus.

 

Agree with @Sulev.
Also: I'm not sure offhand what variety would be most likely for your region, e.g. A. muscaria var. flavivolvata or var. guessowii and so forth. If you do an internet search on "Amanita muscaria California mushrooms" likely your regional var. options will come up.

 

I found more today in a different part of the same area. Much paler in color but in better shape.