1. In 1821, California became part of Mexico after gaining independence from Spain. July 28 marks the anniversary of the signing of the Treaty of Cordoba, which formally recognized Mexico's sovereignty over California.

2. On July 28, 1866, the Transcontinental Railroad was completed with the driving of the "Golden Spike" at Promontory Summit in Utah. This connected California to the east coast by rail, greatly impacting transportation and commerce in the state.

3. In 1945, a B-25 bomber crashed into the Empire State Building in New York City, killing 14 people. Among the victims was L.A. Dodgers pitcher Hugh Casey, who was in New York to attend a baseball game. Casey had previously played for the Brooklyn Dodgers and helped them win two National League pennants.

4. July 28, 1976 was the start of the deadliest heat wave in California history, which lasted six days and resulted in over 200 deaths. Temperatures in some areas exceeded 110 degrees Fahrenheit, causing widespread power outages and overwhelming emergency services.

5. In 1990, California Governor George Deukmejian signed into law the California Clean Air Act, which required the state to reduce emissions of pollutants from motor vehicles and other sources. The law has been credited with improving air quality in California and inspiring similar legislation in other states.