The butterflies were pretty agile. As long as I kept my speed below 35, they could dodge my car or ride the slipstream up the windshield and over the car.
By the time we got to the ridge of Ben Lomond mountain, we were in a blizzard of butterflies. I once drove this road the other way during a snowstorm. The feeling was much the same, but in shades of gold instead of white and gray.
When we rounded the bend and headed back down into the forest, the butterflies vanished.
Our piano teacher was astonished to hear of the butterfly storm less than a mile from her home. She helped me rescue several insects that had gotten caught in the grill and the windshield wiper blades. We got a good look at the butterflies, and I memorized their wing patterns so I could look them up when I got home.
The California tortoiseshell is relatively rare most years, then has huge population explosions like this one.
Ceanothus is the host plant for the California tortoiseshell's caterpillars. The adults feed on ceanothus and manzanita nectar. The top of Ben Lomond mountain is chaparral, thick with ceanothus and manzanita.
I also noticed that the yerba santa was in bloom and wondered if it might be the butterfly host plant.
We often see magical sights up on the mountain: coyote, snow, a red fox, red-shouldered hawks, band-tailed pigeons, the California sister butterfly, and all the plants of the chaparral in bloom.