I also find it interesting that they'd use wood in general service. Yards, sidings, switches and other specialwork, OK, but not the main track. Of course, modern ties aren't the creosote-dipped wonders they used to be; now they're usually pressure-treated wood that lasts a lot longer than the old stuff.

Wood ties can last quite a while if the overall track construction is good. The older track on Sacramento RT has wood ties, and seems to ride smoother with less side-to-side bumping (holds alignment better?) than the newer track on concrete. The wood ties in many areas look like they're originals installed in the 1980s - very few tie replacements, and where they are replaced it's usually with a short stretch of concrete. On the other hand, there seems to be a frequent tie-replacement schedule on the otherwise unrebuilt parts of the adjacent freight line (Placerville Branch) - about every 5th tie or so every year. Since the Phoenix line is likely to have more traffic than the occasional scrap yard train we get, I'd expect a heavier grade of construction.