Currently, California relies disproportionately on high-income earners.  As can be expected, states that rely the most on the wealthy now have the largest budget gaps to fill as the downturn in the economy has left these state governments scrambling for cash.  As the 

The danger of relying on the top earners is that  the wealthy have wildly fluctuating incomes, which means that California state revenues will also fluctuate.  If funds are not set aside in a rainy day fund  during economic booms (which they haven’t been) then during an economic downturn, tax revenues dry up.  One of the major concerns of Governor Brown’s newest tax proposal is that it relies, to an even greater extent, on the wealthy–adding 3% to California’s top tax bracket.