In 1851, Ernest Kidder, a partner, and five mules were packing supplies to their mining partners on the Salmon River from Trinidad, Calif. The trail was narrow and high above the river.
The mules carried 50-pound sacks of flour on their sides and 125 pounds of salt pork on the pack saddles. Kidder watched in horror when one mule stepped on a spot of slick clay and slid down a steep slope.
Kidder said the mule tucked its head between its back legs and rolled like a wagon wheel. At one point it bounced 10 feet in the air and crashed into a large oak tree. The sacks burst, turning the tree white with flour.
Kidder went down the slope to make sure his poor mule was dead and recover what he could of its load. After fighting through the brush, he found the mule standing there looking at him and then making its way unaided back up to the trail.
Trying to pick up some of the flour, Kidder found it concealed a live rattlesnake, so he abandoned the flour and picked up some salt pork instead.
Source: Kidder, Ernest R. "Story of a Siskiyou Argonaut." The Siskiyou Pioneer in folklore, fact and fiction, vol. 4, no. 5, 1972, pp. 99-100.