Emergency Medical Services



When disaster strikes, local medical and health resources may be inadequate to meet the demand. The Medical/Health Mutual Aid System is designed to address this issue by facilitating the distribution of regional, state, and/or federal resources to the area(s) in need.

In California the Medical/Health Mutual Aid System is facilitated by grouping counties, referred to as Operational Areas, together to form six Mutual Aid Regions. Within a region, if disaster strikes, resources are distributed from the unaffected Operational Areas to the affected one.

San Joaquin County is part of Region IV. Other counties in Region IV include Alpine, Amador, Calaveras, El Dorado, Nevada, Placer, Sacramento, Stanislaus, Tuolumne, and Yolo.

View a detailed map of Region IV (Updated August 2015) (Designed to print 42" x 36")

View a map of the 6 Mutual Aid Regions


Medical Health Operational Area Coordinator (MHOAC)
An individual appointed by a county Department of Health Director/Local Health Officer who is responsible in the event of a disaster or major incident where mutual aid is requested, for obtaining and coordinating services and allocation of resources within the Operational Area (county).

Click here to see a diagram that illustrates how the System Coordinators orchestrate the Medical/Health Mutual Aid process.

OES Region IV Multi-Casualty (MCI) Plan

The current OES Region IV Multi-Casualty (MCI) Plan is comprised of 3 interdependent manuals: Manual I - Multi-Casualty Incident Field Operations; Manual II - Multi-Casualty Incident Control Facility Operations; and Manual III - Medical/Health Mutual Aid System.

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TitleRevision Date
Manual 1 - Multi-Casualty Incident Field Operations (PDF)June 1998
Manual 2 - Multi-Casualty Incident Control Facility Operations (PDF)February 1998
Manual 3 - Medical/Health Mutual Aid System (PDF)March 2005