The best I could find so far is the Orange Curtain in February 2008.
Basically it is a 3 mile course (or 10K out and back) you do either 5 times (shorter 50K variant of the race) or 10 times (if you are completely nuts). "100K" sounds totally scary to me as it is a three-digit number. But if we convert it into miles the number becomes more reasonable and manageable: “just” a 60 miler with a couple of bonus miles at the end :)
Overall elevation gain is “blistering” zero as the course is completely flat :)
I will totally miss mountains and all the scenery but on the other hand no need to carry camera all the way (or otherwise constantly regret I did not care to take one).
This should be something similar to those 12h and 24h rat races.
The best part of it the race is held in Cerritos, which is pretty close to us.
The worst part – I never tried anything like this before but I guess this out-and-back course should bore me to death :)