ive got a remington 1100 12ga. not exactly something id want to pack around. thought about the mossberg JIC but id have to practice shooting from the hip, and still prolly wouldnt feel comfortable taking on a bear with it.
Then the question is, how fast can you haul ass? 
some can run as fast as 30mph. i can run pretty fast, but not that fast.
from arizona dept of game and fish...
To discourage a black bear, immediately:
Alter your route to avoid a bear in the distance.
Make yourself as large and imposing as possible if the bear continues to approach. Stand upright and wave your arms, jacket or other items. Make loud noises, such as yelling, whistles, and banging pots and pans.
Do not run and never play dead.
Give the bear a chance to leave the area.
If the bear does not leave, stay calm, continue facing it, and slowly back away.
If a bear is in your yard, scare it away from inside the house, keeping the door closed.
In an emergency: Black bears usually avoid people, but if they start to associate people with food they may become aggressive. On the rare occasion that a black bear becomes aggressive, do the following:
If a black bear attacks, fight back with everything in your power – fists, sticks, rocks and E.P.A. registered bear pepper spray.
notice it says dont run, and fight back
You only have to out-run the guy next to you. 
the only reason im worried about bear attack, is that im usually alone, increasing chances of attack by 10 fold. bear attacks usually happen to 1 or 2 people.
i plan to do a 23 mile back country trip in the spring, solo, in bear and cat country, where the bears and cats are not used to seeing people. i need something just in case.
ponds from now on.