This route differs from the Primary Route in that you continue up Shoemaker Canyon Road until it terminates after the second tunnel.
The road itself thins down to a footpath. You follow this path until it shoots up the side of the primary eastern ridge. Follow this to the ridgecrest (takes awhile). Once atop the ridge, simply follow it up to the summit of Rattlesnake Peak.
There are a few frustrating false peaks along the way. They add to the fun.
Upon my visit, there was no real trail there, aside from what animals left behind. The foliage was thick in places. I've been told it's a bit easier to follow in several ascents after mine.
The ridgeline and surrounding views are really beautiful in winter. Activity dies down, and it's a bit more quiet and peaceful.
Bring lots of water. Bring more than enough. It can get hot here in the summer, since you're at lower altitudes, and the ridge is pretty steep.
In the winter, this peak gets snow, but ice is not likely. Trekking poles would be a good idea in any season, as the soil is loose.