Obama joined Chavez' widow, Helen Chavez, at the headstone, and placed a "Cesar Chavez Rose" on the grave, honoring the diminutive labor leader who became an internationally recognized voice for the poor and disenfranchised. He died in 1993.
The monument is a 3-acre parcel of land at Nuestra Senora Reina de la Paz, the headquarters of the United Farm Workers.
The president's visit was designed in part to shore up support of Latino voters in the upcoming presidential election, the Los Angeles Times reported Monday.
Polls show Obama can expect about 70 percent of the Latino vote, and many of the country's fastest-growing Latino communities are in hotly contested "battleground" states, but Latinos tend to lag behind in voter turnout, the newspaper said.
"My dad still talks about the day he held a UFW flag while marching in Cesar's funeral procession," local activist Maricela Mares-Alatorre of Kettleman City, Calif., said. "The memory I'll pass down to the next generation is this: I was there when the president of the United States came to La Paz and declared it a national monument."