The San Gabriel river has lots of junk, from pull tabs to screw tops. But the good part is that you can still find gold nuggets there, especially after a heavy rain storm along parts of the river. The gold tends to be very small, so I would have to recommend the 4x6 shooter coil. Two reasons the 4x6 coil, one it is more sensitive to smaller objects and two you will be able to get around trash a little better. You will have to dig almost everything to find gold, unless the iron probability is 90%, I would question even 60% probability whether it was gold or not. I would also recommend 2 books, one by Joseph F. Petralia called Gold Gold and the other is Where to find gold in S. California by James Klein the books will help you read the river better for a better chance at finding some gold. Good luck