Spot quiz: Of the dozens of rivers that flow through California, how many are completely undammed?

Answer: Just one. (Read on to find out which.)

'This is the real thing, you know? This is where I evolve.'

But that number would likely be zero, were it not for a law passed by Congress 50 years ago: the Wild and Scenic Rivers Act.

For Tim Palmer, a naturalist, photographer, and author of 26 books, including "California Rivers" and "Wild and Scenic: An American Legacy," the date is etched into his consciousness as firmly as his own birthday. For nearly 40 years, Palmer has chronicled and photographed America's rivers, with an eye to their role in nature and society. And frankly, he's a little worried.

It's impressive to see Palmer — at a sinewy age 70 — haul his 75-pound canoe off the top of his van and onto his back as if it were a day pack. This day, the setting along Putah Creek in Napa County was scenic, if not especially wild, just below the towering Monticello Dam. But anywhere he can get on the water makes him giddy.

"Rivers are the lifelines to almost everything that exists," says Palmer. The fact that about 1,400 dams, large and small, now dot the California map is testament to human dependence on them for water, electricity, and recreation.