BR575 is, I believe, the Goodyear/Maricopa Fire station in Mobile, unless they've changed things around in the last 3 years. Depending on where their call was, it could have been South Mtn or White Tank. South Mtn is the default for Maricopa, but if they were out near Gila Bend, they may have needed to use White Tank. It's my understanding that Mutual Aid channels are Narrowband, making it even more amazing that you heard them in Yuma.