Complex sentence: The historical record of major earthquakes affecting California includes basic seismologic data on the largest earthquakes occurring between 1769 and 1989, The Forces that shaped the earth in the past are still occurring today, as best demonstrated by California's earthquakes.
Split into simpler sentences: The historical record of major earthquakes affecting California includes basic seismologic data on the largest earthquakes occurring between 1769 and 1989. The forces that shaped the earth in the past are still occurring today, as best demonstrated by California's earthquakes.