Axolotls
are legal in California. (However the law may have changed in the last three years since I moved to the Midwest...) "Mudpuppies" are not. As per the laws there, this is an attempt to protect native species of tiger salamander as various species of tiger salamander larvae are used as fishing bait.
here is some links:
http://www.dfg.ca.gov/wildlife/species/nuis_exo/ferret/ferret_issues_table6.html
http://www.californiaherps.com/salamanders/pages/a.t.mavortium.html
I have legally purchased true ambystoma mexicanum in San Diego, and have seen them stocked at both momNpop and big name pet shops many many times. In fact my current stock of axies are third generation descendants of my original two breeders purchased in La Mesa, California in 2000.
As for their legality state by state, there are only two states with documentation eliminating the sale of axolotls as pets: Hawaii and Maine
It is commonly believed that axies are not legal to own privately due to the all too common misnaming of them, and the inabillity of poorly trained pet trade employees to tell the difference between species.