Why did some large Sierra Nevada mammals become less common during the 20th century?

Large mammals in the Sierra Nevada became less plentiful during the 20th century primarily due to increased human presence in the region.1

The expansion of human activity, which accelerated following the mid-19th-century gold rush, led to significant environmental changes, including the development of infrastructure, urbanization, and the damming of streams to meet water and power needs. These disturbances to the natural habitat, combined with growing human occupancy, have placed pressure on wildlife populations. While some species, such as the mountain lion, have shown signs of a comeback, others like the fisher and wolverine have become rare, and mountain sheep are now restricted to the southern portion of the range.21