The rock says:
IS NEAR THE SOUTH
WEST CORNER OF THE
BUSINESS DISTRICT OF
ASTORIA, OREGON, THAT WAS
DESTROYED BY FIRE IN 1883
AND AGAIN IN 1922
The rock sits just past the street sign in the middle of the photo.
Here's the sign (at the corner of 9th and Exchange). If you follow Exchange for a few blocks, you'll come to another of the fire's landmarks, which I'll show another day. I read about it, but I don't think it has a marker like this corner has.
I took this photo of the Labor Temple a few paces down 9th Street toward the river. You can see clearly the deco influence in this building and the tan building on the right, which fronts on Commercial, the main street of downtown Astoria. Like many of the downtown buildings, the date, 1923, is stamped on the Labor Temple along with the building's name. Keeping up with the times, the Labor Temple Diner & Bar has its own page on Facebook. And here's an earthy review of the venerated landmark. I suppose "language or content warning" is appropriate on the second link, but I think it gives a true picture of what you'll find there, and it has a photo of the inside.
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