Locations in the northern (Mount Helix) part of the CDP use La Mesa addresses, while locations in the southern (Casa de Oro) part use Spring Valley addresses.

Informally, Casa de Oro is often considered to be a part of Spring Valley.

In 1872, after a scientist discovered a European snail (Cornu aspersum, formerly Helix aspersa) living on a small mountain, Rufus King Porter, the founder of what is now unincorporated Spring Valley, California, named the peak Mt.

[2] Then in 1885, the United States Postal Service rejected the use of two words for a post office name, so Rufus submitted just the name Helix and also became the first postmaster in Spring Valley; the Helix Post Office was operated out of his home.

He bought the Porters' ranch and also acquired neighboring properties, accumulating about 500 acres (2.0 km2).

Bancroft hired workers to help develop Helix Farms, planting orchards and building structures for his ranch.

[4] According to the United States Census Bureau, the CDP has a total area of 6.9 square miles (18 km2), all land.

The 2010 United States Census[21] reported that Casa de Oro-Mount Helix had a population of 18,762.

There were 7,249 housing units at an average density of 1,057.8 per square mile (408.4/km2), of which 5,018 (72.3%) were owner-occupied, and 1,925 (27.7%) were occupied by renters.

In the California State Legislature, Casa de Oro-Mount Helix is in the 38th Senate District, represented by Democrat Catherine Blakespear, and in the 71st Assembly District, represented by Republican Kate Sanchez.