H.R. 3120 directs the Department of Defense to review how it calculates cost of living adjustments (COLA) for military personnel and civilian employees stationed in California's 19th Congressional District, which includes areas like Monterey. The bill expresses congressional concern that current COLA calculations may not accurately reflect the significantly higher costs of housing, transportation, groceries, and healthcare in California compared to the national average, and that the existing formula may be outdated or incomplete. Within one year of passage, the Under Secretary of Defense for Personnel and Readiness must submit a report to Congress examining the data collection methods, whether military commissaries and exchanges should be factored into COLA calculations, and whether certain areas should receive increased adjustments. The report will also compare how COLA is determined for different California locations, with a focus on whether Monterey's military commissary affects its adjustment rate. The bill carries no specific funding or implementation timeline beyond the one-year reporting requirement.