One thing you should also consider is that your layout plan might be difficult to elevate. My outdoor layout is only partially elevated because fully elevated track would limit access to areas of my yard. Elevation of at least part of your layout will make it much, much easier to place rolling stock on the track. Utah gets hot as does Las Vegas where I live, your track will get longer in the summer and shorter in the winter, joints will loosen if you don't solidly connect them together (like rail clamps). I chose let my track float, with only roofing nails pinned into the gravel below to hold it. It moves slightly with the temperature fluctuations nicely. I have also found moving my rolling stock on and off the track to be a pain over time. Although O Gauge is not as hearty outdoors as G Scale, you may still want to incorporate a Train Shed to protect your equipment during the nice weather while removing it during bad weather. The size of your lashups may dictate a really big Train Shed, I am building mine right now 24ft long with 4 tracks side by side. This takes up a bit of real estate. Just giving you some insight from some of my mistakes.
Enjoy,
Chris Sheldon
