Would this be good base rock?

South Florida is base rock. It'll do the job.

I can't see the pic very well but some of the pieces look fairly solid. If that is the case and you're definition of base rock is using the rock as "foundation" then it will work fine. I would imagine that stuff is loaded with organics and would strongly suggest that you cycle it outside of your tank (or at the very least pressure wash it) before adding to your display.

Like Greech said if you just mean "foundation" when you say base rock that rock seems fine.

Personally though, if I were to start a new tank I would go for the eco saver rock at Bulk Reef Supply. There are some other really good sites out there too. The cool thing about that rock is that it will pretty much fit together like legos and you can make some really nice and natural looking aquascapes, usually without any epoxy or anything. Even if you do make a a crazier aquascape, it still manages to look natural because those rocks do so well at fitting together. Also, since they are so pourous, placing coral frags is easy and you can usually get it to exactly where you want.

The rock in your picture is pretty much what I have in my tank and I regret putting it in because placing corals and making a natural looking reef scape is really hard. With this rock, you can easily see all the seams where the different pieces are and it just kind of looks like a pile of rocks in my tank right now. So until I have corals growing all over the place and covering most of the seems its gonna look like this. Just my 2 cents though.