At one point we stopped at a map to see if there was someplace nearby to stop, get out of the heat and get something to eat. A local rider stopped and suggested that we head over to the National Horticulture Society, pick up some water and turn back! Yep, it was so bad that a complete stranger told us it was time to turn back. :-)
We met James at the Horticulture Society and he escorted us to their kitchen and hooked us up with ice water. He invited us to stay in the a/c as long as we needed and shared a little of the history of River Farm.
After we cooled off we headed back and found that....it was all downhill. We practically coasted the whole way back to the bike shop. Once we turned the bikes in, we had just enough time to grab a bite to eat before we took the water taxi back to National Harbor.
It wasn't quite the ride I had pictured in my head and I would've loved to go all the way up to Mt. Vernon...but there's not much you can do when it's 104 degrees and you're on the verge of heat stroke... I'll have to save the rest of the trail to ride another day.