I would say 12" is the average size of trout. The lake is good fishing, I always troll it and use a medium to large willow leaf with a green wedding band. Jones is a good lake, i have caught some good sized trout there. If you want really good fish, Ross lake by hope but its a far drive
I have always had good fishing at Weaver, small fish though, but lots of them. I recently went to Alloette lake and caught a good number of Kokanee's. I havent fished Jones yet, to many yahoo's there, so I dont normally camp there.