Actually, there are several tunnels through the grapevine route that carry water from northern California. Mining enginers have been dealing with poor tunneling conditions for centuries and have a a pretty good handle on the challenges involved.

The zig-zag, while less direct, creates fewer engineering problems, reaches a growing population center and does not substantially increase the travel time through mountains. I am not familiar with the Palmdale airport plans but if likely, it would be a good fit.

Also note that Metrolink would serve as a feeder line to the Palmdale junction. Communities on I-5 in the mountain area (ie Gorman and others) can reach Palmdale by road with reasonable drive times.

My thoughts anyhow.