I had been across it dozens of times on bike, on foot, and in 4×4, but never realized it was there. An aqueduct. The reason I had noticed it this time were the recent signs of machinery used to clear the ditch of debris and vegetation.
I followed it to the north where it joined up with a stream and a diversion. Then I followed it south where it became elevated as it crossed a gulch. The water sitting in it was still half-frozen.
After judging the structure sound, I carefully walk out on it and shot a photo downwards.
The weather was turning bad, so I didn’t follow it further. But I did check it out on the topo maps and learned that it fills a series of lakes nearby. The lakes appear to be on private property.