Please see Mr. Patterson's comment below.  Evidently all Tern initially pictured in this post were Elegant Tern. 

Which was bad news for the status of my Identification skills but good news for my life-photo-list, and this post.

Mike Patterson's post about the ELEGANT TERN hanging around the Hammond boat basin caused me to run-in-place most of the night while I waited for a reasonable hour to begin the chase.  When I arrived at the basin, I was astounded by the fact that there was not a parking place to be had in the entire area. The Coast Guard personnel on-hand where very friendly and helpful despite the chaos they attributed to boaters competing to get into the river before daylight. Obviously it is a big deal when Buoy-10 to opens to salmon fishing on the lower Columbia River. When I gassed-up in Warrenton and commented on the congestion to the attendant. He told me avid sport fisherman spend $300 dollars day on fuel - and they fish 2 to 3 times a week during the season.  I now feel a lot better about chasing this bird :-)

I have to thank a couple of other people for pointing out the (difficult but approachable) location of the tern on the riprap near the pilot-boat dock. First and foremost to Linda for taking the time to come get me off my station near the water as I waited for a possible fly-by, and Cassidy who's scope the three of us relied on to make a positive ID.  

Despite the two hours I spent on high-alert for TERNs, I found that I was at times unsure of what I was seeing. That may be due to the fact that I was looking at both immature and adult plumages, or more likely just the result of my lack of experience with terns in general.

Elegant Tern - My favorite pose:

Immature Terns: 

Going back through all of the photos that I kept from this trip I think I may have found a good comparison between Elegant and Caspian Terns. They are both flight shots although not in the same frame for size comparison.

Elegant Tern; versus

Caspian Tern:

Either an adult feeding an immature bird or just two immature birds playing, 4 photos:

Elegant Terns in Flight (6 photos):

Below is an interactive map of the Hammond Boat Basin (click-on the "A" for directions):

Here are a few other images taken while I was waiting for the light to improve:

Brown Pelican:

Adult Heermann's Gull:

California Gull:

First year Heermann's Gull: