New York — A 1950 Neal Cassady letter that inspired Jack Kerouac’s spontaneous style in On the Road is heading to auction where it’s expected to bring up to $600,000.

Christie’s is offering the letter of 18 double-sided pages on June 16.

It’s known as the “Joan Anderson Letter.” It was believed lost until it surfaced in 2012 in the discarded files of a now-defunct San Francisco publishing house where it had been placed in a “to read” pile.