In a letter to Homeland Security Secretary Kirstjen Nielsen and Pentagon chief Jim Mattis, Brown said 400 additional National Guard Troops would join the 250 assigned to an ongoing program to combat transnational crime.
'This will not be a mission to build a new wall.
Across California, 250 members of the state's National Guard are conducting what the governor called "counterdrug missions", including the 55 at the border.
The California Guard members may be deployed at the border, the coast and elsewhere statewide, Brown said.
Until Brown's letter on Wednesday, California had been the only border state that had not authorized a deployment of National Guard troops to support Trump's border security mission.
Trump has said that he wants as many as 4,000 guard members to assist Border Patrol agents until a wall is built. But not all of them will go to the border, and none will be "enforcing federal immigration laws". In comparison, the governors of Texas, New Mexico and Arizona were more enthusiastic in their offers of help.
U.S. Border Patrol has assessed that 303,916 immigrant apprehensions took place along the Southwest border in 2017, the lowest it's been since 1971 and down from a high of 1.64 million in 2000.
The federal government must agree to the terms before the troops would be deployed. President Trump blasts Oakland Mayor Schaaf, Gov.
The California Guard program now employs 250 personnel, including 55 at the California border with Mexico. Where the additional personnel are located "will be dictated by the needs on the ground", Brown spokesman Evan Westrup said in an email.
And the governor insisted in his letter that Trump's public pronouncements on border threats were misguided - pointing to statistics that show the number of detained immigrants in California is at its lowest point in almost 50 years.
The governor stressed in his statement that the troops will not be used to "round up women and children or detain people escaping violence and seeking a better life".
Brown qualified those requirements noting that there is no massive wave of migrants pouring into California. He added those were the same reasons he agreed to similar targeted assistance from President Bush and Obama in past years.