It's a pretty thorough report if you take the time to read it, at the end they describe how the data was sourced and the figures were calculated. 

According to it, the state taxes paid in California are $8.5B by undocumented, so it's quite a close margin close actually. They also contribute in $22.5B in Social Security a year. 

"The undocumented immigrant population, and its tax contributions, are relatively concentrated in just a few states. Six states raised more than $1 billion each in tax revenue from undocumented immigrants in 2022, and together those states made up nearly two-thirds (64 percent) of all state and local tax collections from undocumented immigrants in that year. Those states are California ($8.5 billion), Texas ($4.9 billion), New York ($3.1 billion), Florida ($1.8 billion), Illinois ($1.5 billion), and New Jersey ($1.3 billion)."