Harris arrived at Los Angeles International Airport shortly before 4:30 p.m. and was greeted by officials including Monterey Park Mayor Henry Lo, Los Angeles Mayor Karen Bass and county Sheriff Robert Luna.
She then rode in a motorcade to Monterey Park, where she placed flowers at a growing memorial outside the Star Ballroom Dance Studio, where Saturday night's shooting occurred.
After paying her respects, Harris laid the bouquet down, and walked to the press, delivering short remarks-- urging that the country take action to address the all-too-common tragedies.
WATCH: Monterey Park in anguish as stories of victims emerge: 'It feels like it happened to your family'
Monterey Park in anguish as stories of victims emerge: 'It feels like it happened to your family'
"I have had the unfortunate experience of visiting many of these sites, sometimes within days of a massacre like this," Harris said. "We will always, as a compassionate nation, mourn for the loss and pray for those who survive and are recovering. But we must also require that leaders in our nation who have the ability and the power and the responsibility to do something, that they act."
Harris praised California for their work on smart gun safety laws, but stressed that Congress must take action for the country as a whole, and "have courage to do the right thing."
Harris, who lives in Brentwood, was in the Southland last Friday, touring a stormwater-recovery and groundwater-replenishment project in Sun Valley to tout drought-mitigation efforts.
ABC News and City News Service contributed to this report.