I am unsure of the James Doyle one though I know where it is. Scott rock is dedicated to a local rider who rode with many of the core TOT riders for many years prior to his passing a few years back. Whenever there was a group ride through that trail he would launch that rock. After his passing some of the guys went out there and had the rock engraved and dedicated it to him.
...if you call riding with a chainsaw riding solo. You mighta had some beers with you that day too. If I recall correctly. Lol.
I got some vids of riding Vietnam with Scott. He could friggin ride. I have a pic of him launching Scott Rock too. Smooth on everything. And got real fast too. RIP.