What is the legal test for establishing probable cause in an affidavit?

As we stated in People v. Terrones (1989) 212 Cal.App.3d 139, 146, 260 Cal.Rptr. 355: "The standard by which a magistrate must determine whether an affidavit is sufficient to establish probable cause ... is explained in Illinois v. Gates (1983) 462 U.S. 213, 238-239, 103 S.Ct. 2317,

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Probable cause "is a fluid concept-turning on the assessment of probabilities in particular factual contexts--not readily, or even usefully, reduced to a neat set of legal rules." (Illinois v. Gates (1983) 462 U.S. 213, 232, 103 S.Ct. 2317, 2329, 76 L.Ed.2d 527.) It is less than proof beyond a reasonable doubt (id. at p. 235, 103 S.Ct. at p. 2330); less than a preponderance of the evidence (ibid.); and less than a prima facie showing (ibid.).