Problematic Prius (Prii?)

What's the plural of Prius?   If it's like cactus, it should be Prii.  Regardless, they're included in Toyota's string of issues and problems.  This seems like a good time to discuss the technology and it's limitations.

I purchased a Prius last March when my Echo started to eat it's transmission.  It had had a hard life.  I looked around and realized that the Prius was practically the only vehicle that got better gas mileage than the Echo.  Thanks to the recession, they were easy to purchase.  I've really enjoyed mine, although the lack of gears to shift was an adjustment.  I routinely get over 50 mpg.

Irony Gap

Sunday my trail running group staged a run over the Charoleau Gap, a pass over the San Maniego Ridge.  This route is a well known jeep trail.  I brought up the rear taking photos.  The turnaround was at the first crossing of the Canada del Oro, which drains the valley between San Maniego and Oracle Ridge--

That was about 9.7 miles into the run.  On the way back as I neared the Gap, I started to encounter 4 wheel drive vehicles--