This seemed like a pretty large specimen of Bull Kelp (Nereocystis luetkeana). But it turns out that Bull Kelp can get much larger.
For example, the longest blades hanging down in the photo above are probably ~2 meters (~75 inches) long...but they are known to reach lengths of up to twice that length (~4 meters or 157 inches)!
The large float (pneumatocyst) at the top of the stipe/base of the blades also seemed pretty big:
This pneumatocyst was ~11.5 cm (~4.5") inches in diameter...but they can reach diameters of ~15 cm (~6") across.
In case there's any confusion, in the photo above the pneumatocyst is on the right. ;)
We'll have to keep searching for an even larger Bull Kelp specimen!
Photographed on 29 September 2016.