My buddy Bassin' Rich and I got together for some kelp fishing at Island Grissom and had a great time! Bassin' Rich even caught a White Sea Bass, one of the most elusive and sought after fish in the SoCal Saltwater scene.
Island Grissom is just a few yards off the shore but it offers a true "open water" experience without having to actually go out into open water... LOL!
Google Maps calls the parking lot where you set up the "Alamitos Beach Parking Lot" and you get to it from Shoreline Drive. It's a real hike from the car to the water, but it's worth it. Be sure you wear something on your feet.
I do want to point out that Island Grissom is a working oil platform and the service boats zoom in and out of their little dock area all the time, so you need to be careful and get past that spot as carefully and quickly as you can.
As far as the marina goes, I've been told that you're not supposed to fish there, but Rich paddled up to one of the harbor patrol guys at the entrance and he told us to go ahead... so we did!
Here's my Tips and Tricks for Island Grissom - Happy Fishing!