The Western States 100 is a 100 mile endurance run across the Sierra Nevada in California, from Squaw Valley near Lake Tahoe to Auburn near Sacramento. To get a flavour of the race, you should read Dean Karnazes' Ultramarathon Man.
The 2010 race took place this weekend, with a massive amount of build up on the excellent iRunFar website, in particular Bryon Powell's great super-relaxed interviews with most of the leading runners, for example Anton Krupicka who goes into the Western States unbeaten over 100 miles, and with a huge amount of training under his belt as documented on his incredible blog Riding the Wind.
The other 3 main candidates for winning the race were Kilian Jornet of Catalonia who ran 800 km across the Pyrenees in 8 days only 3 weeks ago, Hal Koerner, 2 times defending champion, and Geoff Roes from Alaska also unbeaten over 100 miles.
At 50 miles, all 4 of these runners were still together, until Kilian Jornet and Anton Krupicka began to pull ahead. However later in the race Jornet faded and Geoff Roes came through to break the course record, finishing in 15:07:04.