Identification of this spider?
This is very likely a species in the Amaurobiidae superfamily, and I agree appears to be Callobius severus (the hackled-band weaver or the hackledmesh weaver).

 Source: Bugguide.net 

 Source: Kyron Basu 2012 
Moldenke et al. 1987 provide a key to spiders of the Pacific Northwest. Importantly, they note:

adult genitalia are necessary for identifying species and separating
Callobius from Amaurobius.


For example, here is a picture of Amaurobius ferox (Hackledmesh Weaver)


 © Danny Steaven 2008 

I've seen numerous sites conflate this species with C severus and actually I've seen sources that identify them both as the &quot;Hackledmesh Weaver&quot;.

So although the OP's specimen strongly resembles Callobius severus, a scope is necessary to truly identify to species. This Penn State page provides good information regarding these similar looking species in the superfamily.

Callobius and Amaurobius species have similar life histories and behaviors. They are most often found in damp locations under bark, leaf litter, and stones, as well as in woodpiles and other protected areas.

Stephen Ellis Lew (2011)  produced an atlas to the genitalic morphology of the Callobius genus, and he proposed a morphological diagnosis that is more consistent with principles of homology than those previously in use. [See the link for his dissertation on the subject].
Callobius severus
Description:

Cephalothorax and legs = reddish to dark brown [Source].
Abdomen = dark to light grey with fine hairs; often with large, bilaterally mirrored paler spots.

Ecology:

Nesting woodland species commonly seen in the Pacific Northwest

McIver et al. (1990) suggests that this species of spider is one of many that is characteristic of young forests.


Is it Dangerous?:

Not according to this Penn state website:


The one verified record of a bite by an immature Callobius species resulted in pain, itching, swelling, redness, and nausea.


Vetter &amp; Antonelli provide evidence for how to differentiate this species from the &quot;more dangerous&quot; hobo spider.




in the side view, the palp of Callobius males has large, conspicuous, pointed projections (Fig. 7).