County Meaning or gist and origin

Where the Spaniards rode their horses along the coast to establish missions, lots of places received the names of saints:
San Francisco: Saint Francis
San Benito: Saint Benedict
Santa Clara: Saint Clare
San Mateo: Saint Matthew
San Luis Obispo: Saint Louis Bishop
Santa Barbara: Saint Barbara
San Bernardino: Saint Bernard
San Joaquin: Saint Joachim
San Diego: Saint Diego

Some counties got named for people:
Kern: Named for Edward Kern, artist, explorer and map maker
Lassen: Named for Peter Lassen, rancher and prospector
Humboldt: Named for Alexander Von Humboldt, epic scientist
Glenn: Named for Hugh J. Glenn, big time wheat farmer
Stanislaus: Named for the baptized name of native chief Estanislao
Marin: Named for the baptized name of Chief Huicmuse – of the sea
Mendocino: Named for Antonio de Mendoza, first ruler of New Spain colony
Solano: Named for the Catholic Father Francisco Solano and the native
chief who was baptized with the same name

A bunch of counties got names of objects; words in Spanish, English, Galician, or native languages:
Santa Cruz: Holy cross
Nevada: Snow capped
Mariposa: Butterfly
El Dorado: Gold
Sacramento: Sacrament or Lord’s Supper
Calaveras: Skull
Plumas: Feathers
Orange: Orange
Monterey: Mountain king
Trinity: The Christian Godhead of the Father, Son, and Holy Spirit
Madera: Wood
Imperial: The empire, relating to
Los Angeles: Angels
Ventura: Good luck and fortune
Kings: Kings
Placer: Deposit of precious minerals
Inyo: Place of great spirits
Tulare: Sedge and reeds
Alameda: Public walkway and promenade
Fresno: Ash tree
Merced: Mercy and grace
Amador: Lover
Sutter: Shoe maker or cobbler
Napa: Fairy valley
Yuba: Maidu village named by the Spanish for the abundant grapes ubas

These counties are named for their geography:
Contra Costa: Opposite coast
Lake: Lake
Alpine: Of the high mountains
Riverside: By the river
Del Norte: Of the north
Sierra: Chain of mountains, like a saw
Butte: A hill with a flat top and steep sides off by itself

A few counties are the names of native peoples who inhabit the area:
Modoc: Folks from Northwest California and Southwest Oregon
Shasta: Folks from Northern California by the big tall volcanic mountain
Colusa: Colus is the name of a native tribe living on the west side of the
Sacramento River, of the Wintun peoples
Mono: Native Paiute people who live by Mono to Owen Lake

Lastly, some county names are ultimately mystery and lost to history:
Tehama: Land of shallow rivers, salmon and floods?
Siskiyou: Bob-tailed horse or six stones???
Sonoma: Moon or nose???
Tuolumne: Many stone houses or straight up steep or ???
Yolo: Full of rushes or the name of a chief???