Doña María Ygnacia López de Carrillo (January 31, 1793 – February 28, 1849) was a Californio ranchera.

After Joaquin's death circa 1836, Ygnacia and her nine unmarried children traveled north by ox-cart over 500 miles (800 km) to Sonoma, where they stayed with her son-in-law Mariano Guadalupe Vallejo.

[2] In 1841, Governor pro tem Manuel Jimeno confirmed her possession by granting her 8,885 acres (3,596 ha) of land, designated as the Rancho Cabeza de Santa Rosa.

Ygnacia supervised the farming on her rancho, where wheat, barley, oats, corn, beans, peas, lentils, watermelons, and muskmelons were grown.

A Franciscan outpost named Assistencia Santa Rosa de Lima was begun on the site in sometime around 1829, but the project was abandoned due to secularization.

In 1950, Archbishop John Joseph Mitty purchased the land for building the Cathedral of Saint Eugene and its associated school.

[6] In 2005, the City of Santa Rosa gave tentative approval for a developer's plan to build up to 165 units on the parcel and spend more than $300,000 to prevent further deterioration of the adobe itself.