Yosemite National Park is in California's Sierra Nevada, about three hours east of the San Francisco Bay Area.
Prismatic light is caused by refrection as different wavelingths of light take different paths of light through a material. Rainbows also involve reflection, as that prismatic light bounces within a water droplet and returns the the viewer. Normally circular polarizing filters are used to block polarized, reflected light, but they can enahnce rainbows by being rotated into an "off" position, allowing the polarized prismatic light but blocking some of the randomly scattered light in the scene. Since the returning prismatic light is limited by the number of water droplets returning that light, there are additional techniques that cna increase the quantity and area of the returning prismatic light.
I had seen this rainbow the day before, but returned the following day when I could capture it a little higher in the waterfall. We also saw the secondary rainbow, higher and less bright and with reversed colors, but it wasn't bright enoughh to put on a good show against the ambient light.