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Lurking beneath the city of is an underground waterway that you would never know was there unless you've done a bit of exploration throughout the area known as the Mill Slough. Nearly a hundred years ago a bustling city was growing in the middle of a very marshy area. Rains and high tides often caused flooding in the area, and it was nearly impossible to get from one side of the town to the other without getting your feet wet. Throw in lots of mud and the scarcity of land for new buildings, and you can see what the residents were confronted with, and they new something had to be done.
Well, in 1921 the residents decided to literally enclose the Mill Slough inside a tunnel which was then buried. Alas, no more marsh and mud lands. To show the extent the city went too they also built a tide gate at the bay front to prevent the high tides from reaching the area. Now that it is out of site you might wonder if the waterway still functions.
Happily the answer to that is a yes. The tunnel still collects water from runoffs and the empties it into the bay. It also provides a path for migrating salmon looking to reach Blossom Gulch. At this point the creek still remains active and the plants and animals flourish. Here you can explore the trail and see the connections between upland and wetland areas of the watershed.
You can find four plaques, all rather historic which mark areas of particular importance. You'll want to find the Mill Slough Tide gate, the point where Mingus and Blossom Creeks converge, the site of the bridge which was used before the slough was buried, and the upstream entrance to the tunnel.