Political factions will imply that indigenous people were ‘basically wiped out’ when they justify grants for reparations, create new government agencies, increase agency payrolls, etc.. When they want to receive benefits or increase representation, then Census numbers (http://factfinder.census.gov/servlet/QTTable?_bm=y&-geo_id=04000US06&-qr_name=DEC_2000_SF1_U_DP1&-ds_name=DEC_2000_SF1_U) showing about a million living in California alone are used. That doesn’t even count additional millions of people who are unaware that they may be also descended from the original tribes.
Many died when native and western cultures mixed, but most died from diseases (like Ishi) from ‘friends’. Once immunities were developed, native populations have apparently increased to levels higher than had been before first contact.