Sutro's Mules

Sutro's Mules were noted for their strength and stamina sturdiness and hardiness. For decades they were an essential tool in making the mines profitable by pulling train loads of rich ore. They worked hard and lived the greater part of their useful lives as an integral part of the subterranean world.
Where would the mines be without them?
The Honorable William Keyser one stated:
"Mules contributed more to the prosperity of Nevada than the Silver Kings.