Why is the Gresham, Oregon area so murdery, by episodes?

Gresham sits on Portland's eastern edge, in Multnomah County, and the towns in this hotspot fan out from there: Oak Grove eleven miles away, Skamania twenty-one miles off across the Columbia in Washington, Colton twenty-three miles out in the farmland. Portland is what ties them together. Oak Grove is twenty minutes from it, the Gorge town about forty-five, the logging village about fifty, and Gresham itself just outside. Colton began as a Swedish logging community and still has half a dozen churches and no taverns.

The dates run from 1972 to 2017, so the four episodes are spread across five decades, but the count isn't evenly spread. Episode 631, from Oak Grove, accounts for nine of the fifteen murders by itself, across cases in 1972 and 1987. Episode 246 adds three. Episode 454 adds two, and episode 240, the one that happened in Gresham proper, adds a single murder from 1989.

Gresham takes rank 21 overall and second place in Oregon mostly on the strength of the towns around it.