What road is this? According to the monument at the Allegheny/Washington County line that inspired the cache, it's the William Flinn Highway. On paper, it's Washington Pike, aka State Route 1009. Google Street View says it's Morganza Road (which it DOES become, farther South at Hendersonville and down to Canonsburg). -- and they wonder why people get lost in Western Pennsylvania?
As for William Flinn (Google him!), he was an influential construction and building tycoon AND Republican Party bigwig who got the contract (big surprise!) to build this and other major roads and projects. If the name rings a bell, there is also a William Flynn Highway aka Rt. 8, North of the Allegheny River. Same guy, but they misspelled his name over there. Oops. Follow the link in the "Related Web Page" entry for the Wikipedia article about William Flinn.
The site is best approached from the North (Bridgeville) . You'll see the monument on the right, and then there is a nice pulloff space just on the other side of the intersection with Fawcett Church Road. Take care; you'll need to walk very near the road back to the cache.
Be safe. Don't do a U-turn back to Bridgeville. Continue South for re-entry to I-79, or for access to the Montour Trail if you want to find caches there.