For most of the Western United States --- points west of the 100th latitude --- the limiting factor is not land but water.
The city of Los Angeles has a watershed which extends 1,500 miles eastward, to the western extent of the Rocky Mountains. The reason much of the Western US appears more as an island archipellago than a continuously inhabited terrain is because there simply isn't enough water to fill taps, flush toilets, and run showers, let alone grow food or provide range for livestock on an unirrigated "dry-land" basis. Even attempting that proved a major environmenal disaster, the Dust Bowl of the 1920s and 1930s.
The city of Los Angeles has a watershed which extends 1,500 miles eastward, to the western extent of the Rocky Mountains. The reason much of the Western US appears more as an island archipellago than a continuously inhabited terrain is because there simply isn't enough water to fill taps, flush toilets, and run showers, let alone grow food or provide range for livestock on an unirrigated "dry-land" basis. Even attempting that proved a major environmenal disaster, the Dust Bowl of the 1920s and 1930s.