In many areas of California, you'll see tracks and scat but hardly ever a bear, and then it's the hind end rapidly vanishing into brush.

The habituated bruins often use the national park trails - I've been ten feet from a bear a couple of times on trails, and in response to the yelling and trekking pole waving, the bear has glanced at me as if bored stiff and walked away slowly.

I had a bear sneaking up on me in Yosemite with her cub - I stood up (sandwich in hand, that's what she was after) and stared, and she walked away.

Checking on the food storage rules for the area you're traveling to will shed light on the behavior of the bears - Yosemite will levy up to a $5000 fine for not having a canister from the approved list, and the parking lots are full of bear lockers. Go to campgrounds in national forest areas and there will be lockers with broken latches, and the camp host will instruct you to stick stuff in your trunk (huge no-no in Yosemite where the bears rip open cars).

I don't even bother with bear spray in California, but if I were heading to Montana, Wyoming or other states with a grizzly population, I'd pick up a canister before hitting the trail.