Choosing the Site
Features you want or features you need!
Picturesque view for the wife
Mrs. Pilgrim wanted a view of the valley below and a scenic look at the sunset. This one could prove to be an important point. Perhaps she has figured out that if she spends the rest of her life looking at the sun as it sets, her eyesight will eventually go bad enough to where I look more attractive as time goes on.
Going cheap doesn't mean it has to be cave
Mrs. Pilgrim wouldn't have gone along with this site for even a minute. She made it clear that fighting javelina and mountain lions for this site every night wouldn't make for a very relaxing living environment.
Functional slope for drainage
Unless you want to hire a contractor, or rent and haul expensive machines to dig a hole and trench, you need to find a spot where you can have a slope of between 1" in 4' and 1" in 8' to your septic tank and drainfield. If you can't achieve a slope between those two figures, there will be problems with your drain pipes. On this site it was easier to lay the drain pipes right on the ground (which is essentially a rock slab) then cover it with dirt hauled from someplace else on the property.
Unless you like to dig....
This would've been a terrific site to build, due to it being a major stop along the route of the Monarch Butterfly migration, but since it was down in a flat valley, it would have taken some serious machinery to pummel deep enough through the rock bed that lies only 6" below the surface to place the septic tank far enough down to allow the proper slope.