California Governor Jerry Brown has signed a state senate bill, allowing a gender-neutral marker on birth certificates and driver's licenses starting from 2019.
California thus became the first state in the US to allow a "nonbinary" gender to be marked on birth certificates, Xinhua news agency reported.
The so-called "nonbinary" gender means not exclusively male or female or a combination of two or more "genders."
According to the Gender Recognition Act approved on Sunday, California will offer a gender-neutral option on state documents for those who are transgender, intersex and others who are not identified as male or female.
The law, published on the government official website, also made it easier for people to change their gender identity on official documents.
"Existing law authorises a person who was born in this state and who has undergone clinically appropriate treatment for the purpose of gender transition to obtain a new birth certificate from the State Registrar," the bill read.
The Golden State is now also the second state in the US to allow residents to be identified by a gender marker other than "F" or "M" on their driver's license.
Oregon and the District of Columbia had earlier issued the gender-neutral option on their driver's licenses.