Sorry, I do not remember the size of the spider or the burrow.

Trochosa sp. would be my guess. They have these extremely shallow burrows, usually under some object.

I chose Hogna over Trochosa for several reasons. The medial stripe on the carapace in this specimen extends forward to the AME, while in Trochosa it doesn't reach that far front (or if it does it isn't so well defined). Also, the stripe looks narrower to me than what I've been seeing in Trochosa. It is very much the same as in, for example, H. helluo:



Also, the heart mark is darker than the background color of the abdomen in Mike's specimen; in Trochosa it is usually lighter than the rest of the abdomen.

Kaston, 1981, mentions that "During the cocooning period the female [Hogna helluo] may often be found under stones in shallow burrows lined with silk."

A couple of weaker reasons: If the spider is Trochosa sp, then those are very small ants (which is possible, of course). Normally-sized ants (bl ~ 1 cm) have jaws large enough to effectively surround and bite through the leg of a Trochosa. I'm assuming the ants aren't very small.

I was assuming that the seed in front of the spider in the 2nd picture was not a dandelion but was larger.

The Trochosa egg sac is so large and round that the spider usually has to stand more upright, on its toes, holding its abdomen up to carry it than what we see in the second picture (though a picture taken from a better angle would have helped confirm that). I've seen a Hogna that carried it the way Mike's specimen does.

Trochosa with egg sac:

I'm making some assupmtions here, of course. :)

It would help if the Mike Silva could tell us how large this spider was. An adult Hogna helluo is almost twice the size of an adult Trochosa.

I also thought it looked like Hogna, but that doesn't mean much coming from me.

Ant Size - I made the opposite assumption about the ants. I was thinking they look like those tiny pavement ants.

Spider legs - Do you see how the spider's legs have those whitish 'bumps'? What are those? Does that mean anything?

I'm not sure what those might be. I think I see similar markings on the front leg of this H. helluo, but I don't know if they mean anything as far as using them to identify the spider:

They might be. I've had spiders and ants fall into the same pitfall trap, and sometimes the ants grab the spider and don't let go even when both are put into alcohol. I have a vial containing a wolf spider and ant from a couple of years ago, and the ant is still hanging on to the spider's leg! Talk about a death grip. :)