Perhaps this shouldn't be surprising since the entire area from the high Sierra down into the Sacramento Valley used to be home to both black bears and grizzly bears.  California even adopted the grizzly in our state flag and state seal.  However, the Gold Rush triggered a rapid rise in the human population and a terminal decline in the grizzly population.  The last grizzly kill in northern California was recorded in 1922, though their record extended to 1926 in southern California.

The remaining species, the black bear (Ursus americanus), is the most common and most widely distributed of all bears.  Though its name is "black", its coat can be black, brown, or cinnamon and can vary in color even among individuals within a single family.   This color usually is embellished by a small patch of white on its breast.

Black bears are admittedly large animals, but they're actually petite by bear standards.  Here's how they compare with grizzlies:

 

Black bears are most active in the part of the day centered on twilight in totally natural circumstances. However, these highly intelligent animals adapt easily to either stress or opportunity in their environment; the result is that they easily change their foraging habits and can become either nocturnal or diurnal (active at night or during the day).

With 5-toed feet, their forepaws leave tracks that look like those of a barefoot human.  In eating habits, they're omnivorous -- they'll eat all sorts of stuff!  Their natural diet includes berries, grubs, fruit, carrion, eggs, honey, and small animals.  Many years in the foothills offer an abundant supply of acorns.

Their unnatural diet includes garbage and all sorts of human food.  Yosemite's bears have become particularly notorious for learning new ways to break into parked cars, even if only for a midnight snack of potato chips.

Black bears have very good hearing,  eyesight on a par with humans, and a magnificent sense of smell.  Their lifespan can be 30 years or more, and their running speed in a short distance can be 30 mph or more.  Running away is often how they react to the sight and sound of humans. Typically they pose no threat to people if left alone, but it's best to leave them alone from a very respectful distance.

Typical locations for black bear dens are beneath downed trees and in small caves.  They hibernate through the winter, sometimes waking but mainly staying in a "deep sleep" state.  Females begin mating around age 3 1/2, and give birth to one litter every other year.  Each litter usually includes two tiny cubs born in late January or early February; they weigh only 7 to 12 ounces at birth!

Cubs accompany their mother through most of their first two years.  During this time she protects them from predators and male bears while they focus on non-stop eating and playing.  She quickly trains them to climb a tree in response to her woof-like danger signal.  Also, the easiest way to be charged by an otherwise timid black bear is to take up a position between mom and her cubs.

By the end of their second spring the cubs leave their mother.  They usually stay together briefly, then separate in the fall to take up the solitary habits of an adult.  An adult male may range up to 50 miles daily in its territory, which can easily be more than 100 square miles.  Sierra mountain topography tends to produce irregularly shaped territories with a maximum dimension of about 15 miles.  Females occupy much smaller territories, generally around 10 square miles.

Modern black bear territory is in the high and mid-Sierra, but they do sometimes reach lower elevations.  Within the last few years they've visited the Peninsula Campground and Mammoth Bar.  And Waterford history so far has shown that we are in bear country at least once every decade!

Distribution map of American black bears is from www.bearden.org, a web site presented by the American Zoo & Aquarium Association Bear Advisory Group.

The bear track photo, showing clear tracks left in moist soil and showing the full gait, is from the JuneauAlaska.com web site.  Each forepaw print is immediately behind the hindpaw print left by the bear's next successive stride.

Hibernation:

There are two main types of hibernation that have one significant difference.  In both cases the animal's heart rate and respiration drop substantially from their levels in active animals. Waking from hibernation tends to be a relatively slow process.

In bears' hibernation body temperature only drops a few degrees from its active/normal level.  Bears can remain in this state for extend periods but are likely to wake occasionally.  In the other type of winter hibernation, usually called "true hibernation", body temperature drops dramatically, usually to a temperature very few degrees above freezing. This is more common among small animals, which tend to wake much more frequently to serve bodily functions.

Although bears are not "true hibernators" by historic use of the term, biologists are not unanimous in this classification.  It's clear that bear hibernation is physiologically as significant as "true hibernation".  This seems to be a principle that needs better names.

Two other related principles are torpor and estivation.  Torpor has similarities to hibernation, but the animal can awaken rapidly. An example is hummingbirds:  Almost all of those that overwinter in the Sierra foothills are Anna's hummingbirds, which enter torpor every night. Estivation is a tactic for surviving extremely hot weather instead of extremely cold weather.

Sense of smell and intelligence, a personal anecdote:

Many visitors to parks such as Yosemite in past years have seen graphic demonstrations of bears' acute sense of smell through unfortunate events in campgrounds and parking lots.  These often have demonstrated bears' intelligence, foiling attempts to safely store food. They usually also have demonstrated the bear's physical power, especially when it converted a steel-bodied car to something resembling wreckage.

My example turned up a bear with finesse.  During a 2-day hike from the Yosemite Valley floor to Half Dome and back my pickup truck stayed in a parking lot.  It's equipped with a shell, whose hatch was locked, and inside were two plastic bins with tight-fitting lids.  What I had forgotten in one was an uneaten half of a bear claw (the pastry), secluded inside a paper bag.

At the end of the hike, as evening darkness fell, the truck looked normal except for a note on the shell's hatch.  It was the rangers' standard form announcing that a bear had ransacked my truck, something of a shock because everything looked as I had left it.  Even the hatch was still locked!  On looking closer I found a cluster of dirty bear pawprints and one small scratch from a claw.

Apparently the plastic-windowed hatch flexed enough that the bear could pry it open without damage while it was locked.  Inside, one plastic bin's lid had a tear in its heavy-duty plastic, one on each side, neatly arranged exactly where a human would grasp the lid to open it.  The contents were as I had left it, except that the paper bag that had
contained the half bear claw was torn and empty.  Apparently the bear had extracted everything but had damaged practically nothing, and a ranger had put the goods back.

There are far more remarkable stories of bears' ability to smell food.  There are stories of bears using at least as much intelligence and skill to go after even "properly stored" food. So far though I haven't found a story of a bear being as skilled and polite as this one was in securing a goodie from a locked vehicle.

Weight quotations for bears are typically far less consistent than might be desired.  One problem is that the weight of individual animals varies considerably depending on the season. There can be substantial individual variation, just as with humans:  Bears can have their equivalents of little wimpy guys, 300-pound NFL linemen, and everyone inbetween.
The maximum weights quoted in the table are intended to be fairly reasonable, they fall short of heaviest-bear records reported for exceptional animals.

Another issue is that bear populations in different locations can tend to have different weights.  "Lightweight" weigh-ins for black bears have come from eastern Tennessee, the Great Smoky Mountains, and the San Gabriel Mountains on the rim of L.A.  In contrast, some of the heavier populations have been reported from Mammoth Lakes and Alpine County, in our northern Sierra area.

Uncertainty and wide variation in reported weights is common even in information from consciencous reliable sources.  It may start with careful biological studies in a given area at a given time, and these numbers may be propagated by others as general weight quotes for a species of bear.  Because of that, it's hard to get a coherent "measurement" of weights.

To work around this I surveyed a lot of information through Google searches, assembling lists of weight ranges and "typical" weights.  In each list I discarded the extreme high value and the extreme low value.  For minimum/maximum weights I quoted the minimum of the remaining listed "minimum" values and the maximum of the remaining "maxima".  The quotes for typical weight are rounded mean (average) values of the remaining data.

For black bears sources tended to have a bimodal distribution.  I suspect that this corresponds numbers from different seasons -- the table in this web page may show minimum weights in the spring and maximum weights in autumn, at opposite ends of hibernation. The typical weights I quoted for black bears may be very slightly low for local populations, though data is spotty -- the best northern Sierra data samples that I found were from Alpine County and from the Mammoth Lakes area.