I planned and followed through with a dive expedition to Delgada Canyon submarine trench up in Humbolt County several years ago.
Do a search and you will see the typo map of the canyon, pretty radical to say the least!
https://images.app.goo.gl/CoAymKKHBnZ8WqLz8
There were four of us total. It was VERY remote and we had to trailer a boat to Shelter Cove then take the boat up the coast several miles to find the trench. I originally saw it on a old US Geological survey paper map and thought I just had to explore this place. Nobody to our knowledge had ever dived this particular spot. The rock walls that surrounded the canyon were pretty spectacular with giant dinner plate size scallops hanging off the rocks. We were expecting to see tons of big fish but instead found tons of very small fish, lingcod 2” long and everything seemed to be babies. We realized that this was probably a protected fish nursery and must have been a place where fish would go to drop their eggs. There were also a ton of spot shrimp all over the base mud bottom. It would have been theoretically possible to reach the trench from shore and be in 300’ of water only a few hundred yards from shore, but the problem was there was no shore access, it was a sheer cliff for 1000’ to the beach so boat access only. We did four dives over two days there. It was quite an experience to dive something like that.
Other than that, all the offshore pinnacles off of Mendocino County are all worth exploring. I’ve done my share just cruising along in my skiff watching the bottom sonar and noting any blip that showed up by marking it with GPS. Then at some point later we would go and dive those spots. There’s a lot of radical terrain out there with sheer walls that plunge down to 150’ or more just 50’ or 75’ away from an offshore wash rock. I’ve found huge cracks and swim throughs that are like big underwater cathedrals.
Colby Reef is on the map and not really an unknown spot, but due to the remoteness and lack of scuba support and divers up here I’ll bet it’s been years since anybody has dived on it.
If you want to know about remote spots that are gems to explore and dive, befriend an urchin diver and they might just tell you about a few spots including a few wrecks that almost nobody knows about.
Arena Rock in Mendocino County was probably one of the most spectacular places I’ve ever dived in my life bar none. But Arena Rock has been dived for many years by many people. It’s still hard to get to and even harder to plan a dive there because it’s pretty far offshore with very unstable conditions and currents. I lucked out every time I was there that it was calm and no current with great vis. Thank god for buoy reports and NOAA forcasts!
