The best inference based on the information provided in the chart is: The mass migration of forty-niners transformed San Francisco into an economic hub practically overnight.
This conclusion is supported by the dramatic increase in population from just 850 in April 1848 to 25,000 by December 1849, indicating a rapid influx of people due to the Gold Rush. The significant population growth during this time suggests that the Gold Rush had a profound and immediate impact on the city's development and economy.