Travelers to the Pacific Coast in the mid-1800s faced a challenge that other pioneers did not face. This challenge was

dry deserts.

deadly diseases.

high mountains.

winter storms.

Answer: high mountains c

High mountains: The paths upon entering the mountains became rough, very steep, with crossing rivers.

Explanation:

The ground was full of rocks and people could get hurt badly. As the pats were very difficult to pass, without marked routes, people got lost very often.

Aso, there were many more obstacles, like drowning, diseases, guns, dying of thirst, not enough oxygen, etc.