
Born in c. 1822 in Cambo les Bains, a Basque province in southwest France, Leonis arrived in Los Angeles in 1854. He was part of the wave of French-speaking immigrants, primarily Basques, who settled in the area in the mid-1800s. He quickly found work in the San Fernando Valley as a sheep herder, ultimately becoming foreman at Rancho El Escorpion--present day West Hills, Woodland Hills, and Calabasas. Leonis met his wife on El Escorpion in 1859; but contrary to Basque custom, his wife, Espiritu Chijulla, was a Chumash Indian.
When Leonis first acquired the Adobe property, historical notations suggest that an abandoned adobe brick structure from c. 1844 sat on the site. During the 1870s, Miguel and Espiritu moved into the home you see today. The home is constructed of adobe bricks, a common building material used in the region during the period. Miguel had it built as a two-story dwelling with a wraparound veranda, known as the California Monterey Style. He added traditional wood cladding to both the home's exterior and to several interior rooms. The house is adorned with various architectural elements, including Victorian fretwork along the balcony. Several years later, he fully enclosed the rear and northeast portions of the veranda in order to build more interior spaces on both floors. Presumably chosen by Leonis, the original colors of the house were discovered under many layers of paint.

Originally slated for demolition, the Leonis Adobe survives today primarily because of the efforts of a local community activist named Kay Beachy. She recognized the importance of historic preservation early on and spearheaded the official formation of the Los Angeles Cultural Heritage Board. Within hours of the Board's first meeting on August 6, 1962, the Leonis Adobe was designated Los Angeles Historic-Cultural Monument #1and saved from the wrecking ball. Today, only a small portion of the property remains, much of it sold off over the years. In fact, the existing barn, built in 1912, was moved twice to accommodate the 101 Freeway.
In 1889, Miguel Leonis died in a wagon accident while traveling to downtown Los Angeles over the Cahuenga Pass. He was thrown from his wagon, which was heavily loaded with firewood, and crushed underneath its wheels. Despite a 30-year common-law marriage to Espiritu, Leonis willed the majority of his assets to relatives in France. Espiritu challenged the estate in court, a highly unusual step for a Chumash Indian woman in the 19th century. After a 16-year protracted legal battle, and just seven months before her death in 1906, Espiritu won her case.