August in Oregon, is Blackberry season, and locals are seen picking wild blackberries on city streets, and practically everywhere along country roads.
We have so many bushes at our beach house that we pick ,and pick and it seems like there will be no end to the bounty.I bake blackberry pies every week in late July and August. Sooo good!
Blackberries are everywhere in the Portland area, and to a lesser extent all over the northwest. The most common type was introduced and is now considered an invasive species because they take over just about any open space and to a lesser extent forest land.
Therefore, you can pretty much find them everywhere. Most commonly they are around in late summer, but the exact season depends a lot on the amount of rain and average temperatures during the year.
The vines are easy to spot: they are the long thorny vines that stick out of just about any pile of weeds and brush in wild lands around Portland.
However, if they are beside the roads it is quite possible that they have been shot with any number of assorted poisons by the highway department to kill them. You do not want to eat those, unless you are certain that they have not been sprayed recently.