If it was a ball diamond or playing field they'd at least have some justification. But this is a narrow strip of grass half way down the river bank. It's not a groomed lawn. It's not in front of a fancy building, it's not even in front of a house. Regardless of the gophers it's rough ground. (This is just north of the Broadway Bridge, on the East side of the river.)
This is poison that kills small animals. So it's going to kill mice and voles and shrews as well as gophers. And then it'll end up on the systems of the foxes and coyotes and hawks and crows. And the rest will wash into the river and from there who knows where.
I'm sure the manufacturer will tell you it's safe. Given the history of pesticides I wouldn't put too much faith in that. For example, check out this article from High Country News. Rozol doesn't sound like a pleasant chemical, nor does it even sound like the best option.
If I had kids, I don't think I'd want this stuff around. And I've seen numerous people walking their (often small) dogs along here. I can't imagine the poison is too healthy for them either.
So given all the downsides and risks there must be a highly important reason to be doing this. Surely the city isn't doing it just because ... it's what they do? Our roots may be in agriculture, and farmers might be in the habit of killing gophers (and coyotes and beavers and whatever else they might imagine gets in their way). But this isn't a farm, it's the city riverbank. And we don't have any horses or cattle to worry about breaking their legs in a gopher hole.
So much for "nature city".