The Buick Gran Sport or GS was a high-performance option package available on a number of Buick models, including the Riviera, Skylark, Century and Wildcat. A special version of one model was given the package's name as its model name.

Buick touted the California as "The Distinctive Personal Car for Americana on the GO". The merchandising creation of the West Coast's Mickey Garrett, the California GS became one of Buick's entries into what is now often known as a junior musclecar. The intent of these autos were to provide the visual impact of the era's supercars with the low maintenance and price of a more economical car, while maintaining reasonable performance levels. When reviewed with these thoughts in mind the California GS delivered quite nicely. They were fitted with the small block GS drivetrain and the exterior received the full treatment including vinyl top, chrome moulding package, GS emblems, and special California scripts.

1967 was the maiden year for the California GS. It was available in California only and was not advertised nationally by Buick. Built on the thin-pillar coupe chassis it came equipped with the 340 ci/260 hp engine and Super Turbine 300 transmission. Bench seats were standard and accessories were kept to a minimum to help keep the price down. Car Life tested one in their June issue and ran the 1/4 in 16.7 seconds at 81 mph, they also recorded a top speed of 105 mph. The article contains a lengthy description of the car and how it performed during testing, it is a must read for anyone interested in learning more about the '67 California GS.

Mid year 1968 saw the official introduction of the California GS, and it is frequently knonw as a '69 model. Buick asked "Why settle for less when the California GS, built especially for YOU, costs no more?" Exclusively designed for Golden State motorists, Buick advertised the car nationally as a high performance family sports car at an economy car price. Though the car was not included in Buick's yearly catalog it was shown in a two-page black and white fold out brochure. Custom California GS emblems again graced the rear fenders while GS ornamentation could be found in the grille and sail panels. The drivetrain included Buick's new for '68 350-4 V8 with 10.25:1 compression and Rochester (GM) 4GC Quadrajet four-barrel (four-choke) carburetor, producing 280 hp and 375 ft-lbs. of torque. The two-speed Super Turbine 300 transmission (driving a 3.23:1 rear axle gear, designed for highway cruising) and bench seat interior were again the only choices. Buick also added chrome plated wheels and air cleaner lid to the two-door thin pillar coupe. Tires were 7.75 in (197 mm) on 14 in (36 cm) rims.

1969 was the last year of production for the California GS. The car was for the first time featured in Buick's big brochure. A two-page color picture of the thin pillar coupe and pictures of the again standard bench seat interior were included along with equipment descriptions. Tom McCahill tested the car and recorded a 0-60 time of 9.5 seconds and a top speed of 110 mph. Again the car came with Buick's 280 hp 350-4 engine but now it was mated to the new Turbo 350 transmission. Custom California emblems again graced the rear fenders and the rear marker lights were plain red without Buick's normal 350 or 400 script. Vinyl tops, as with previous years, were standard fare with the California's distinctive GS logo on the sail panel.