Where others work hard to create a vacuum and reduce the chaos of life, [Robert Altman] enjoys creating a micro society while he is shooting, one which has a virtually autonomous existence, in which each member has a role to play, even those who will not end up appearing on screen. He makes his actors and technicians live and behave and act the way his characters would. While for McCabe and Mrs. Miller he may have had to build the small town of Presbyterian Church from scratch in the snows of British Columbia, [in California Split], for most of the scenes, he had existing sets available to him and his team, and it was just like going off on a spelunking expedition. The environment did the rest. Indeed, the shooting at Mapes Hotel in Reno gave all the participants an opportunity to try their luck day and night at poker, baccarat, and the slot machines, whether in the lobby with the regulars or in the sky room, where Leon Ericksen meticulously reconstructed the ground-floor decor. One can only imagine the comings and goings between the two levels. In such an eclectic pandemonium, in which professionals (actors/gamblers) and amateurs (actors/gamblers) were completely intermingled, it quickly became impossible to tell the difference between the real casino and the copy, and the extra-filmic location from the stage, illuminated by the sunlights. This constant Pirandellism, miraculously controlled by the master, is assuredly what makes Altman’s films such a rich and full sensory experience.
Michael Henry Wilson writing on California Split for Positif, February 1975 (translated from French and republished in Positif 50 Years)