Found this looking around tonight.

http://209.85.173.104/search?q=cache...lnk&cd=2&gl=us

Avy control with military recoilless rifles and howitzers first happened in Utah at Alta in 1949. The National Guard supplied the ordinance.

Some gems from the article:

"The Forest Service also
occasionally shot their recoilless rifles from the
back of pickup trucks; however, in the late 1970s
Forest Service snow rangers performing
avalanche control in the mountains above
Ogden, Utah miscalculated and overshot a ridge
and the round landed in and partially destroyed a
house being constructed in an Ogden suburb. "

Cool read if you are into this sort of stuff.