Update. First, After inspection we found that the vertical stand pipe is 8" and the horizontal drain is 6".
We built an 80 foot long ramrod with 3/4" pvc as suggested by Rjackson. We worked the long ramrod in the horizontal and a ten foot piece in the standpipe working from a kayak. By adding water, we were able to free up the clog. Amazing how much silt, leaves,and small twigs flushed out of that pipe. I can still see a couple small pieces of tree branch at the bottom of the vertical pipe, but all the soft material that had accumulated is gone for now. Next heavy rain, we will know for sure.
Now we need to figure out the best way to build a trash rack to go over that 8" stand pipe.
Thanks for all your input.
Bob
