My favorite trout get-away in this area is Clarks Creek. I like to park at the rifle-range parking lot and work my way downstream. Very nice water, makes you think you're miles from nowhere and you're only 20 minutes north of Harrisburg.
From Lancaster, take 283 up through Harrisburg or even 72 to 81. Then take 322 like you're headed to State College but exit off in Dauphin. Go up 225 then turn right after crossing the bridge (there is a PAFBC sign at the bridge). Drive East about 20 minutes until you come to the rifle range on the left - parking on the right below the road level. Easy to miss, so be watching.
Nice water to spend a nice easy day on. If you don't want to walk back upstream, just walk out to the roadway and walk (uphill) back to your parked car.