Thoughts along the Pipeline Path

I took a walk along the Pipeline Path at dusk earlier this week, mostly trying to map out where the side trails enter it, but also taking a few photos. Along the way a few thoughts occurred to me....
In earlier hikes, I had noticed a few areas on the uphill side of the path that seemed like they had been dug out some. Now I realize that these were probably areas that were dug out to use as fill over the brick pipeline as it progressed. In other areas, it was obvious that large rocks had been pushed aside on the downhill side of the path--probably back-breaking labor for those who made the pipeline. I imagine one crew worked ahead of the bricklayers, digging the ditch and heaving aside the rocks, while maybe another worked behind the bricklayers after the arched tunnel was made, digging into the hillside in specific areas for backfill.
Numbered stone markers are found mid-way along the trail. I had previously thought that they go out of numerical order, but from what I could tell the other night they are in order. I think the first one I spotted was "18," and the last was "28." That said, it's clear that at points the pipeline runs 10 to 20 feet off to the side of the trail, on the downhill side, and maybe there are more numbered markers along the actual pipeline.
Finally, there's at least one significant area of ledge that the workers had to get through (just southeast of the "18" marker). I'm just glad I wasn't one of those laborers, though they were probably happy to just to have a job.