How have courts treated allegations of possession of marijuana under the Mental Health Act?

In Cervantes v. Walker (9th Cir. 1978) 589 F.2d 424, a county jail inmate was taken to the jail library for questioning about a recent fight. Defendant left his property outside the library as directed and it was searched. A small amount of "a green odorless substance" was found inside a matchbox. (Id. at pp. 426-427.) The searching officer suspected it was marijuana but had no special training in this regard. He took the substance into the library and asked the defendant what it was. The defendant responded: "'That's grass, man.'" The defendant was placed under arrest for possession of marijuana. (Id. at p. 427.)