The Willamette Valley Project is a series of 13 dams and reservoirs in the Willamette River Basin, with most being "owned, operated and maintained" by the Army Corps of Engineers, or else managed in conjunction with the same. Although dams on the Willamette and its tributaries had existed for some time, the project was completed in 1969.
None of the dams are on the main channel of The Willamette River, which makes sense because the Willamette Valley is broad and flat and building a dam there would flood inhabited areas. Instead, the dams are mostly located in the foothills of the Cascades, with 11 of them being on the east side of the Willamette River, and only two being on streams that drain out of the Coast Range. The dams are usally made with a combination of earthfill and concrete, and are primarily for flood control, both of which puts them in contrast with the much larger, concrete dams on the Columbia that generate electricity. The dams are also in out of the way locations: the Detroit Dam is about 40 miles southeast of Salem, Oregon, and the Foster Dam is about 25 miles southeast of Albany, Oregon. People who drive up and down I-5 can be quite unaware that the dams exist.
I have been aware of the dams for decades, and first visited them when I was still a child, but I didn't think about them too specifically until recently. Recently, while writing about such suburban towns as Keizer or Tualatin, I mentioned, with hand waves, how they "grew rapidly after World War II", which I took to be mostly about changing demographics. Which it was, but it was also due to the fact that the flood-regulated Willamette Valley gave many more locations for people to live. But as is often the case with cheap and efficient infrastructure projects, the people who benefit from them take them for granted. Although, this may change because due to climate change, and also a realization of preexisting seismic risks, the ability of some of the dams to continue to act as flood control is under some question.