Weasel like critters in Washington, with scientific size descriptions are:

Ermines (= Short-tailed Weasel), little
Long-tailed Weasel, little
Mink, medium
Marten (martEn is the mammal, martIn is the bird), medium
Fisher, large
River Otter, large
Sea Otter, large (highly unlikely in a park)
Striped and Spotted Skunk; unlikely to be mistaken for any of the others
Badger, large, east-side only
Wolverines, large, too rare to consider, at mostly high elevations in
the Cascades.

Martens are unlikely in a park (I think it was Marymoor?). They live
mostly up in the mountains. Fishers are a low-elevation associate on the
west-side, but nearly exterminated by previous trapping, and mostly
associated now with remanant old growth forests. They occur at higher
elevation on the east side, but are very rare there, too.

River Otters are pretty big, but many folks are surprised are how small
wild animals are when they see them in real life, so to speak, and the
color description sounds reasonable.

Mink tend to look dark brown to black in color, especially because they're
usually wet, but if they weren't wet, might look medium brown. They're
fairly common around water in the Sound area.

Ermine or Long-tailed Weasel is most likely. They are whitish to
yellowish underneath, but the underneath might have looked yellowish
brown, especially if they were dirty. You can't easily (ever?) tell them
apart in the field. Ermines tend more towards forests; Long-tailed weasels
towards open areas, open forests, or clearings, but both are highly mobile
and opportunistic.

Least Weasels have been rumored occasionally in WA, but no verifiable
records exist.

Kelly Cassidy