Walker Pass is at mile 645.  Wow! I can't imagine hiking that many miles on one trek.  The most Bob and I have done in our section hiking is 240 miles which took us 19 days. This was the section from Donner Pass to Yosemite Valley and the first section we did.

Bob is off to Kennedy Meadows, which is at mile 695.  After that he will head into the High Sierras. The trail goes to 12,000 feet at several points and then to 13,000 feet at Forester Pass.

http://www.pcta.org/pdf/2011-PCT-Map-Brochure.pdf