Early in the morning of September 5, 2002, camouflaged and heavily armed Drug Enforcement Administration agents descended on a terraced marijuana garden. The DEA raid on the Wo/Men's Alliance for Medical Marijuana, a sanctuary for severely ill patients who were using marijuana as medicine, is the riveting opening scene in Weed Land, an up-close journalistic narrative that chronicles a transformative epoch for marijuana in America.

From the 1996 passage of California's Proposition 215, the nation's first medical marijuana law, through law enforcement raids, clinical studies that...