Centro Basco at 13432 Central Ave. Chino is some 5 to 10 miles from Ontario International Airport. 909/628 6410. (The Airport is actually in San Bernardino County. Chino is in Los Angeles County.)
Centro Basco serves family style dinners. The Sunday night I was there the crowd consisted mostly of the family of the owners, another Basque Family and a couple Dutch dairy men.
Excellent oxtail stew and ribs. Similar to the more famous Noriega's in Bakersfield. Get there early and join the regulars at the bar in the front of the building.
They is also a regular dining room at the back of the building.
For a general guide to Basque culture and restaurants get "Basque American? by Nancy Zubiri.