According to the 2008 HOG Touring Handbook...

AZ, Helmet required for under age 18.
CA, Helmet required for everyone, even on a push scooter.
NV, Helmet required.
UT, Helmet required for under age 18.
NM, (just in case you wander over this way) Reflectorized helmet required under age 18. Other than that, probably the least motorcycle restricted state in the union.

Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python