Earthen floor in Mojave Desert considerations

Hello, I'm building a hybrid hyperadobe and light straw clay building and am getting to the point where I'm ready to put in a floor. I'm in the Joshua Tree area and was wondering about what an earthen floor out here might need. Money is quite tight right now, but I need to get a floor in sooner rather than later with winter approaching. My biggest questions are what kind of layers I'll actually need in a desert climate with very little moisture/precip.

The interior is currently dug downed and loosely leveled sand about 10" below where I'd like the finished floor to be. I see most people lay down gravel and a moisture barrier below there earthen levels
Are these layers necessary in a very dry climate? I have a good mix for the floor as I've earth plastered the exterior of the house so far (lime later) with very little cracking and nice rigidity. Would it be feasible to start pouring this mix directly down onto the sand/dirt? I've attached a few photos of what it looks like right now.

What are your thoughts? Thanks!

Looking great. I guess how much drainage work and gravel underlay you do is a matter of your own risk tolerance. What are the chances of a flash flood sweeping across the property and getting into the building? It looks like your finished floor will be pretty much on grade. If it's above by enough that surface flows can't get in, that should take care of things, because you're unlikely to have persistent wet ground as an issue.