Continued extinction of grizzlies:
The Grizzlies continued to disappear and by 1920 the last known Grizzly Bear was shot in the Sierras, not really too far from Yosemite. Obviously, Yosemite wasn't designed to protect Grizzly Bears. By this time, Grizzlies were isolated into small populations all across their range. These became virtual islands of habitat surrounded by islands of unsuitable habitat that had been modified by humans.
Once populations become small like this--and some of these represent only one or a few animals, maybe one or two family groups--once populations become small like that, they become susceptible to those random factors like demographic stochasticity and genetic stochasticity. Those factors interact to reduce the population even more. So, below about 25 individuals, extinction is virtually certain. Joel Berger did a study of Bighorn Sheep populations and their extinction across the west, and all of the populations that were 50 animals or less, all went extinct within the last 30 years.