What is this? An ammo dump?

Hello everyone,
I've been lurking in this group for quite a bit and have really enjoyed some
of the conversations. Now, I am asking for your help in identifying something
that I just found recently:

I live in South Texas near the Mexican border. There is a national park nearby
called "Laguna Atascosa (Muddy Lagoon)" which, by the way, holds the record for
the highest number of diverse bird species that can be seen in one day. This is
a bird watcher's paradise since thousands migrate from the northern states to
the warmer, tropical temperatures that can be found in the Rio Grande Valley of
Texas. Anyways, this area is also the supposed location of where one of the
Spanish explorers (I forget the name) shipwrecked around the 14/1500s. Even to
this day, people are reportedly finding gold coins and other artifacts.

But, what I wanted to ask the group is if they have any information about a
particular army air corps base that used to inhabit this area during WWII. It
is now a country airport with very sparse traffic. But, just north of the base
are a couple of gunnery ranges which you can see here
(http://www.texasairmuseum.com/coast.htm). If you scroll to the bottom you'll
see the base as it looks today. While looking at these gunnery ranges one day,
we came upon a couple of bunkers that were hidden amongst the brush a couple of
miles from the nearest road. You can see our journey he
(http://www.texasairmuseum.com/ammo1.htm) and the second page contains what I
am trying to find out. Since the gunnery ranges were nearby, do you think these
little bunkers held the ammo? Someone once said that these bunkers were
probably hurricane shelters since the base was so close to the coastline.

What do you guys think? By the way, here's a picture of the base during WWII:
http://www.texasairmuseum.com/airacobra.htm

Thanks for any help or research on this base and its history.