5b.–1920-construction-of-building-to-house-rollingmills.-Pacific-Cost-Steel-Coompanys-Seattle-plant-was-by-then-the-largest-steelmaking-facility-in-the-Pac-NW-WEB August 31, 2014 1200 × 545 Seattle Then & Now: The Youngstown Steel Mill Work on constructing a factory “shed” to house a new rolling mill. Dated 1920, by then Pacific Coast Steel’s Seattle branch was the largest steel making facility in the Pacific Northwest. [Courtesy MOHAI]