> I've never seen a ham repeater tower

Lots of photos here from one repeater group:
http://www.carlaradio.net/community/pictures/gallery/

Two example photos (not necessarily typical :->)



> one operator in a disaster area can pass messages to other hams more or less
> in line-of-sight

That's true with VHF/UHF frequencies; that's what the repeaters are for - to increase the line of site. But with HF frequencies, you've got truly worldwide communications from your station if you have a good antenna. We've got a portable antenna that mounts on our van, and from the San Francisco Bay Area, we get all the way to the east coast without repeaters - and with a not good antenna. Here's a photo of it on our van in Death Valley:

As you can see we're surrounded by mountains, but we had chats with a guy in Berkeley and one in Santa Cruz.

In an emergency, I would expect to be able to reach other hams outside California without having to rely on repeaters or other hams in line of sight to get our messages out of the zone of damage. We regularly check in to a net in Reno from our house, the other side of the Sierras.

HF is great stuff, and I recommend that people get their general license (minimum license required for HF), an HF transceiver, and practice using it.