I cannot be certain what is going on with your dogwood without several more close-up photo of the damage, but I've attached some information for you to look over to help you diagnose the problem.
Anthracnose is a common problem in Dogwoods in the Pacific Northwest, and if your tree was damaged last year it is possible it was more susceptible to disease this year.

Here are some links to read about common diseases:
Anthracnose
Leaf Spot Diseases

Here is some very specific information from the PNW Disease Handbook on anthracnose to help you diagnose:

"Cause Discula destructiva, (formerly Gloeosporium sp.), a fungus that overwinters on dead twigs and on leaves on the tree and ground. Tiny brown fruiting bodies (acervuli) of the fungus are easy to see on dead twigs and leaves. Pacific dogwood (Cornus nuttallii) is very susceptible. Flowering dogwood (C. florida) is moderately susceptible but is severely damaged under conditions ideal for disease development. Many but not all cultivars of Kousa dogwood (C. kousa) are very resistant (C. kousa var. chinensis has been quite susceptible in some studies). Bunchberry (C. canadensis), cornelian cherry dogwood (C. mas), and Japanese cornel dogwood (C. officinalis) are thought to be resistant.

Symptoms Most common are large, brown, irregularly shaped blotches on leaves. Often, the diseased area is at or near the leaf tip, centered approximately on the midvein. The blotch often spreads down the midvein, giving a wedge-shaped appearance to the diseased area. Instead of blotches, leaves occasionally have brown spots with dark brown to purple margins. Infected leaves commonly drop before autumn, leaving the tree partially or totally leafless. Affected twigs have sunken tan to brown spots with purple borders, which eventually enlarge and girdle the twig, resulting in twig dieback. Dead gray leaves often remain on the tips of these infected twigs all winter and spring.

Cultural control

• Prune out and destroy infected twigs when possible.
• Rake and destroy fallen leaves from spring through fall.
• Do not let irrigation wet the tree canopy.
• Plant resistant cultivars including the kousa cultivars 'Milky Way' and 'Steeple' and the hybrid cultivars 'Celestial', 'StarDust', and 'Stellar Pink'. "

I hope this is helpful in diagnosing your problem. If you are still unsure after using these resources, please do send us several more close-up photos of the damage (leaves and twigs in particular).

Here are more photos. A neighbor gave me advice that my tree was buried about 5 inches too deep. I removed a layer of top soil around it which you'll be able to see in the last photo. 

Additional 

 These photos do show a sick dogwood. Hilary and I are discussing possible diagnosis. More questions:
How long have you had the tree in the ground here?
Did you plant it yourself or see it planted and are you sure the wrapping was removed, and any twine around the roots?
Please send a couple of more distant photos showing where the tree is growing. If that is a raised bed, the issues could be with the roots.
Tell us about how you fertilize and water it, also. How is winter drainage: any standing water? Thank you.

I believe the tree is a little over 10 years old. I did not plant it. For a long time it was not getting much sun under the tree canopy but that has since opened up. It's up against a retaining wall and I believe it gets very waterlogged during the winter, as it is situated at the base of a hill next to a stream, but it is all subsurface, not standing on top. I have fertilized inconsistently over the past five years. It's had a rough life. Thanks.

Thank you for the additional photos. Our recommendation is to contact a certified arborist for the best chance of saving the tree, but there is no guarantee.
The tree does seem quite small for its age, but it's being confined to what is essentially a container is a likely reason for that. In addition, a container tree would need significant additional water in the summer as well as amended soil in order to thrive, and it sounds like you can't be sure that the tree has had these things, especially early in its life when it is most important.
Here is a link about container trees, which includes a list of trees that would be better suited to a container:
http://extension.oregonstate.edu/gardening/node/1074

If you are unable to have an arborist visit, I'd suggest you give the tree one more year and see how it goes. Your best option may be to choose a tree better suited to that environment and to be sure the soil gets amended, that the tree gets planted properly, and that it is watered amply during its first few summers.
I'm including an additional link that may help you determine what went wrong with the tree as well as some more tips:
http://extension.oregonstate.edu/gardening/dead-tree-or-shrub-post-mortem-analysis