Here is interesting information on John C. Fremont's Lost Cannon from which Lost Cannon Peak is named:
Pete Yamagata's driving directions are still accurate for the most part.
Here's some updated info that includes new sign changes:
Drive through the Marine Corps Mountain Warfare Training Center (MCMWTC) continuing straight on the dirt road.
At mile 1.6 take a left (this road is signed 32059)
At mile 3.0 take a right (a sign says "One Way" with arrow pointing to left - you go RIGHT continuing on road 32059)
at mile 3.7 take a right (do not take the signed road 32059A)
at mile 5.1 take a left
at mile 5.2 you have reached the sign board/flat area/ aka "Woody" GPS: N 38.39591 W 119.5371
Also, if you are considering a link up with Fish Valley Peak (10,571') to the north here are some approximate times going at a moderate pace for a snow-free, mid-July hike.
Starting point is "Woody"
From Woody to Lost Cannon Peak both summits climbed: 2 hrs
Lost Cannon Peak to Fish Valley Peak: 2 hrs
Fish Valley Peak back to Woody: 2.5 hrs
Also, there was no running water/snow pack on this route mid-July 2012. With hot temps I drank almost 4 liters on this hike. Plan accordingly.
Fish Valley Peak sees very few ascents apparently. There were only roughly 28 entries in the summit register that went back to 1994.
The cell phone reception around the MCMWTC seems to be very good. A cell phone that had the MTV of cell providers (Virgin Wireless) got almost full bars near the MCMWTC.
Final note, if you find any old, abandoned live ammunition lying around on the upper elevations of this hike (read: rifle/machine gun ammo), my recommendation is to either leave it where you found it or pack it out and dispose of it yourself. Turning it in to the MCMWTC can be a hassle.