From Mercer to Volant summertime fishing can be tough. There are shady spots for the fish but you can get into some long, remote wading to get there. Kind of like your Black Moshannon area and remote section of Penn's Creek. If rain levels have been good and temps in the moderate range you should be O.K. Just check the stream temps.
From Volant down is the best cool water fishing during the summer. This is the Delayed Harvest Only are so D.H.O. regs apply:
http://www.fish.state.pa.us/fishpub/...s_nw.htm#dhalo
http://www.fish.state.pa.us/fishpub/...rtificial.html
I see they are stocking Wolf Creek in Grove City from the Rt58 Bridges south to the county line. I bet it's good trout fishing early in the season from the dam just below the college to the county line. Take a drive back Greenwood Drive and park by the sewerage treatment plant and fish your way up and down stream form there. Stocking link:
http://pfbc.state.pa.us/pfbc_webgis/...ngDetails.aspx
Wish I could be there with you.