Green’s Dictionary of Slang

Hump, the n.

(US tramp) the Rockies; thus go over the Hump, to cross the Rockies on one’s trek from east coast to west.

[US]G.H. Mullin Adventures of a Scholar Tramp 301: He went over the Hump with us two years ago.
[US]‘Dean Stiff’ Milk and Honey Route 43: Others [...] went down below the Mason and Dixon line or west over the Rockies, called ‘The Hump,’ there to bask in Californian sunshine in the land of Dago red.