Example of a Spanish era grave: Argüello. I think that "M. S. O. de Argüello" refers
to Doña María Soledad Ortega de Argüello (1797–1874), a prominent Californio
'ranchera' and socialite. She inherited and managed the massive Rancho de las Pulgas,
a sprawling 35,240-acre Spanish land grant encompassing much of the southern San Francisco
Peninsula. From modern-day San Mateo and Belmont to Redwood City, Menlo Park, and Atherton.

According to Wikipedia: She was the second wife of Luis Antonio Argüello, a soldier who
served as the first native-born Governor of Alta California under the Mexican Empire.

Majority of graves represent individuals from predominantly Catholic
nations: Italians, Irish, Philipinos etc. I encountered only a few
Spanish names, and not a single Indigenous Ohlone grave marker.