Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
I have heard repeatedly from sources that I trust that the Little J's bed is generally too "cemented" to provide good habitat for spawning. These sources acknowledge that there is some spawning in the stream and in tribs, but not enough to sustain the J's fishery at the numbers we all appreciate.