The Mormon refugees did not find a desert, they found Native Americans living in the Utah Great Basin and proceeded to steal their land and natural resources: http://www.onlinenevada.org/articles/mormons-and-native-amer...

It's not really meaningful to describe people as "rich" or "poor" in the absence of an economy.

Where people are involved there is no such thing as an absence of economy.

At the time (1847), they were not the poorest people in North America.