Travelers on the california and santa fe trails had to cross deadly?

The correct answer to this open question is the following.

Travelers on the California and Santa Fe trails had to cross deadly Forty Mile Desert.

Pioneers and explorers of that time had to cross a dangerous zone in the region called the Forty Mile Desert, a large desertic area located between Truckee River and Humboldt River. People that wanted to inhabit the western lands or were looking for Gold during the California Gold Rush had to cross through this dangeorus desert. Many people and livestock died in the intent.