My grandmother's family is Popa, from Milwaulkee (Poland before that). My grandmother had a brother named Damascus, but he was known as Uncle Dan by my mother. He married Catherine, known as "Cass," and they both ended up in KY. If this is not correct, your Damascus could have been a nephew of this Damascus. The Popa's liked to name their children after brothers & sisters. I'll have to check my tree, but I believe a couple of the brothers (there were 13 siblings total, but a couple died as children & a couple more as young adults) moved to CA.
Do you have a birthdate for your father-in-law?