We have similar soil conditions here, and the ground is already cracking in mid-May so it looks to me like a long dry summer!
I'm in the process of building a flagstone patio about 18'X24' and keep in mind that what I'm doing may or may not work! This is a covered patio and it joins our carport. I dug out the soil about 8" deep and then tried to level and pack what remained. Then I filled the area with "SB2" (what the stone place called it) crushed granite with a lot of granite powder in it. The SB2 is used for driveways a lot in this area and will set up almost like concrete. My aim was for a bed of crushed stone to help keep the flagstone from settling, and to have the floor level of the finished patio above ground level. When I start to set the flagstone I'll use sand over the SB2 to fine-tune the placement of each stone. After my SB2 settles I plan to dig a footing around the perimeter and place a stone border set in concrete to prevent sand/stone from washing out and help keep grass away. This stone border will be at the same height as the finished flagstone flooring.
I hope this works, and I hope it helps...

That sounds great...I might give that a try. My problem is ours won't be covered and there is a tree on the edge of it so we need some drainage to keep the tree from dying. Thanks!

Covered or not shouldn't matter if you have a perimeter established to prevent the sand/SB2 from eroding away from underneath the flagstone.
How close are you wanting to be to the tree? That could be a problem with the tree roots causing heaving as it grows. It could also damage the tree's roots having the patio over them.

You should lay a 4 inch concrete base with an 1" minus falgstone mortered on top of the concrete if you don't want to have any problems with it shifting. If you want a dryset I would recomend using 3/4" minus or flexbase 4" under the flagstone compacted to 95% with a bed of decomposed granite around 1" on top of the flexbase, so you would have a total of 5 inch's of base. If you have any qeustions or need help, or any supplies give me a call at 214-529-0261 we sale and install stone

T.J. James