in reference to zig-zag railways, 1863, from switch (v.) + back (adv.). As an adjective from 1873.
Entries linking to switchback
switch v.
1610s, "to strike with a switch," from switch (n.). Related: Switched; switching. The meaning "turn (off or on) with a switch device" is first recorded 1853 of trains on tracks, 1881 of electricity, 1932 of radio or (later) television. Sense of "shift, divert" is from 1860. Meaning "to change one thing for another" is recorded from 1919. Switch-hitter is 1945 in baseball slang; 1956 in the sense of "bisexual person."
back adv.
"to or toward the rear or the original starting place; in the past; behind in position," literally or figuratively, late 14c., shortened from abak, from Old English on bæc "backwards, behind, aback" (see back (n.), and compare aback). To give (something) back is to give it again, to give it in the opposite direction to that in which it was formerly given. Adverbial phrase back and forth is attested by 1814.