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I'm not very well versed on plant pathogens but this appears to be some type of rose rust (Phragmidium sp) to me.
E: Maybe more safe to say in the family Phragmidiaceae instead of Phragmidium specifically, but Phragmidium might be a good starting spot, especially if you know the rose species it's growing on
Hmmm looks pretty spot on. Unfortunately also looks like it will kill these bushes eventually... Ill have to contact the parks department and see if I can give them a heads up.