Look what I found, set out for the trash! It's a strip of vintage oilcloth shelf lining. It was actually stuck on the back of a strip of vintage linoleum. Talk about jackpots! So I'm guessing the oilcloth is at least 1940s and the lino 1950s (the lino was some of that very geometric style of the '50s).
"What on earth will you do with THAT?" asked my mom on the phone. I don't know. But I couldn't just walk away and leave it for the trash man, now could I?