Eureka Valley so central California on the east side of the state, right Philip?
That is a nice looking collector. It reminds me a bit of some of the umbrella designs and the Russian designs.
Judging by the pot shape under the reflector it is a cone type collector. (like a parabola but with the focal point under it instead of above it, am I guessing right?)
It looks a bit complex to just whack together in an emergency though, and it looks a bit big to haul.
Your original post of a box cooker would be much easier to build, and there are designs for them from at least as far back as the 1930s.
This link is to a pdf that deals a bit more with solar cookers designed for disaster areas and refugee camps in Africa.
It includes plans for a couple of different styles.
Note that the Kookit style can be made with pieces of cardboard taped together if you don't have a single large piece.

http://images3.wikia.nocookie.net/solarcooking/images/5/57/CooKit_plans_detailed.pdf