The Grand Junction resale store said the print, which is signed and numbered 168 of 300, was spotted by a customer at the store who often points out valuable merchandise to management, KMGH-TV, Denver, reported Tuesday.
Manager Bill Atwell said store workers do not know where the print came from.
"Donors are very generous here, we do get some very nice things." He said.
Atwell said bidding for the print reached $550 as of Monday and bidding ends Tuesday evening. The manager said similar prints have been selling for $1,000 online.