In People v. Gardeley (1996) 14 Cal.4th 605, the court held that the primary activity finding was supported by the testimony of a police gang expert who testified as to his opinion that the primary activities of the gang were drug dealing and witness intimidation, both crimes listed in section 186.22, subdivision (e). In People v. Sengpadychith (2001) 26 Cal.4th 316the court elaborated, "Sufficient proof of the gang's primary activities might consist of evidence that the group's members consistently and repeatedly have committed criminal activity listed in the gang statute. Also sufficient might be expert testimony, as occurred in People v. Gardeley, supra, 14 Cal.4th 605. There, a police gang expert testified that the gang of which defendant Gardeley had for nine years been a member was primarily engaged in the sale of narcotics and witness intimidation, both statutorily enumerated felonies. (See 186.22, subd. (e)(4) & (8).) The gang expert based his opinion on conversations he had with Gardeley and fellow gang members, and on 'his personal investigations of hundreds of crimes committed by gang members,' together with information from colleagues in his own police department and other law enforcement activities." (Sengpadychith, supra, 26 Cal.4th at p. 324.) As the court explained in People v. $ 47,050 (1993) 17 Cal.App.4th 1319, 1325, "although an expert's opinion on an ultimate fact is admissible, and may constitute substantial evidence citation, the conclusion by itself does not constitute substantial evidence without an adequate factual foundation. " "Substantial evidence is evidence that is reasonable in nature, credible, and of solid value. While it is the exclusive province of the jury to determine the credibility of a witness and the truth or falsity of the historical facts citation, expert . . . opinion evidence that is based upon a '"guess, surmise or conjecture, rather than relevant, probative facts, cannot constitute substantial evidence."" (In re Anthony C. (2006) 138 Cal.App.4th 1493, 1504.)