Populations within California's Antelope Valley interact with their physical environment (e. g., sunlight and water) to sustain life. What level of life's organization would this be classified as?

An ecosystem

Explanation:

Ecosystem is the functional unit which contains all the individual or organism in a definite place which interacts with their physical environment and also with each other. So the ecosystem is made from interaction between living and non-living things in a specified space volume.

Ecosystem have many communities, communities are made up of many population and population is made up of many individuals / organisms.

Organisms → Population → Community → Ecosystem

Therefore populations within California's Antelope Valley interact with their physical environment classifies the ecosystem level of life's organization.