The billboard is owned by ClearChannel.
The client is the Long Beach Department of Water and Power.
Matthew R. Veeh, Director of Government & Public Affairs, Long Beach Department of Water and Power, say's everyone has signs like this, so it's O.K. for us to a have a sign like this too--regardless of the sign's problematics.
Comment: Given that droughts are an ongoing problem, shouldn't we continue to do rain dances along with everything else?
In fact, one could argue that a return to rain dances might be called for, since Western lifestyles and technologies are causing the drought. Because rain dances go along with reverence for water, which means not wasting it on lawns and pools and so forth.
In short, a rain dance couldn't hurt and might help. So the billboard's message is false as well as stereotypical.
It qualifies as stereotypical because it implies Indians were superstitious fools who did nothing but rain dances. Actually, they conserved their water and thus managed to survive in a harsh desert climate.
This is something we haven't managed to do without huge, wasteful expenditures of water, energy, and other resources. But it's something we may have to (re)learn eventually.
For more on rain dances, see Krauthammer: Scientific Consensus = "Rain Dance" and Indians Perform "Rain Dance" to End Drought.