Cool Vintage Black Satin XL white flannel lined Southern Pacific Milling Co. Safety Award jacket. Hartwell clothing brand. 
MADE IN USA. 
Not to be confused with the SP Railroad, the SP Milling Co. started around 1888 in Central Coastal California, operating from Salinas, San Luis Obispo, Paso Robles, Ojai, Goleta down to Ventura, and closed in 1995. The company supplied lumber up and down the coast to yards like Homer Hayward's even in Pacific Grove; they acquired Santa Barbara Lumber in the mid-20th century. But, yes, back in the day they supplied sleepers for the railroad among the mill products they produced! As the lumber industry changed in California, the company later produced sand, gravel and concrete. 

This is a Safety Award Jacket. Embroidered name on right chest R.I.P. (mebbe the Yellowstone character, lol!) Safety Award on left, with abbreviated SP Milling Co underneath the letters SP logo in a gray round patch.

Still nice and shiny, with a few light blotches here and there, but hard to see, including on knit band below left pocket area. See pix. Black button snaps all work. Knit collar and cuffs have good elastic.
I could not find another item of SP apparel listed anywhere.

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