[Iterated]

Came here to say this. It seems like a lot of the lines are due to the locations of the Federal Reserve Banks. I would also like to note that there are branches of FRBs in Denver, Seattle, Salt Lake City, and Miami, as well as many others, but the ones I mentioned are ones that I find geographically separated from their main regional bank. If you look, even these larger branches of the FRB's seem to be centered in these regions as well. I don't think some of the smaller FRB branches (like El Paso, or San Antonio) have cash services departments (I could be wrong here), but the larger ones do.

To expand on julespitt's comment: Each FRB (and whichever branches of each FRB has a cash department) gets money sent in from banks to be exchanged/counted/cleaned/recirculated/stored/whatever in whichever bank is closest. This explains a majority of these lines. This probably also explains why there's some really defined lines around Seattle, Denver, and Salt Lake City. Even though they are branches of FRB's, they still have cash departments.