The California inspector general says guards at an isolated state prison have created a "culture of racism," engage in an alarming use of force against inmates and have a code of silence encouraged by the union that represents most corrections officers.

The scathing report released Wednesday calls for management and other changes at High Desert State Prison in the northeast corner of the state.

Inspector General Robert Barton says the investigation was hindered by the California Correctional Peace Officers Association, which advised members not to cooperate and sent a disparaging letter to lawmakers.

Union officials did not immediately return messages seeking comment.

The report comes more than a decade after the corrections department tried to stamp out a culture in which prison guards protect one another when they witness wrongdoing.