Command Staff

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Undersheriff Michael Casten

Undersheriff Michael Casten

Undersheriff Casten is a graduate of Sacramento State University with a Bachelor of Science Degree in Criminal Justice Management. Undersheriff Casten is credentialed as a California Senior Executive by the CSAC Institue for Excellence in County Government. 

Undersheriff Casten has been with the Office of the Sheriff for 27 years. He was assigned to the Patrol Division for 9 years as a Deputy, Field Training Officer and Sergeant before promoting to Lieutenant in 2001.  

As a Lieutenant, Undersheriff Casten managed the Communications Unit, Civil Unit, Records Unit and the Internal Affairs Unit. In 2005, Undersheriff Casten was promoted to the rank of Captain and served as the Division Commander of the Technical Services Division. In 2007 he was promoted to the rank of Commander and served as Bureau Commander of the Support Services Bureau before being appointed to Undersheriff in 2011 by Sheriff David Livingston.  

Undersheriff Casten currently sits as a Board Member for the Bay Area Urban Area Security Initiative (UASI), the East Bay Regional Communication System Authority (EBRCSA), and the Bay Area Regional Interoperable Communications System Authority (BayRICS). Undersheriff Casten represents the Sheriff's Office on the Community Corrections Partnership. Undersheriff Casten is a member of the Contra Costa County Chiefs of Police Association.

Undersheriff Casten has served as an executive manager on several large projects for the Office of the Sheriff to include the East Bay Regional Communication System, a two-county multi-jurisdiction 800 MHz P25 digital trunked voice communication system and has served as Chair of the Automated Regional Exchange System (ARIES) during the initial development of that project within Contra Costa County.
 

Assistant Sheriff Chris Simmons - Administrative Services

Assistant Sheriff Chris SimmonsAssistant Sheriff Chris Simmons has been with the Office of the Sheriff since 1998. As a Deputy Sheriff, he was assigned to Detention, County Patrol, and the J-Team specialized patrol unit.  He was also a Detective in the Investigation Division, working in the Special Victims and Special Investigations (Narcotics/Vice) Units; He also served on the Sheriff’s SWAT Team as an operator and designated marksman.

In 2004, he was promoted to the rank of Sergeant, where he was assigned to Detention, the Investigation Division (Special Victims and Homicide Units), Internal Affairs, and as a Team Leader on SWAT.  In 2010, he was promoted to the rank of Lieutenant, where he was assigned to the Civil Unit, Technical Services Division, and Internal Affairs, and served as the SWAT Commander.  In 2013, he was promoted to the rank of Captain, where he was assigned as the Patrol Division Commander and the Martinez Detention Division Commander.

In February of 2018, Assistant Sheriff Simmons was appointed to his current rank and assigned to the Support Services Bureau.  In January of 2020, Assistant Sheriff Simmons was assigned to the Administrative Services Bureau, which includes Capital and Special Projects, Personnel and Finance, Professional Standards, and Training Divisions.  Assistant Sheriff Simmons’ formal education includes a Bachelor of Arts and two Master of Arts degrees in Psychology (Organizational Development) and Criminology, and a Ph.D. in Clinical Psychology.  He is also a graduate of the California POST Command College and the FBI National Academy.
 

Assistant Sheriff John Lowden - Field Operations

Assistant Sheriff John Lowden

Assistant Sheriff Lowden began his career with the Office of the Sheriff in 1994, after serving in the U.S. Marine Corps.  During his career, he has held a variety of assignments.

As a Deputy, Assistant Sheriff Lowden worked in the Custody Services Bureau, County Patrol, Professional Standards Division, and the Investigations Division. Assistant Sheriff Lowden was promoted to Sergeant in 2004 where he supervised in the Custody Services Bureau at the Martinez Detention Facility as well as the Transportation Unit.  He was later assigned to the Technical Services Division to supervise the Civil Unit.  In 2010 Assistant Sheriff Lowden was promoted to Lieutenant and held the assignments of Assistant Division Commander for the Emergency Services and Investigation Divisions.

Assistant Sheriff Lowden was promoted to Captain in July of 2012 and was assigned to the Professional Standards Division, where he managed the Background and Recruiting Units. In January of 2016, he was assigned to the Field Operations Bureau where he managed the Coroner’s and Special Operations Divisions. He completed his tenure as Captain as the Special Operations Division Commander.

In February of 2018, Assistant Sheriff Lowden was appointed to his current rank and was assigned to oversee the Field Operations Bureau; which includes, Investigation, Patrol, and Special Operations Divisions. Assistant Sheriff Lowden holds a Bachelor of Science degree in Criminal Justice and is credentialed as a California Senior Executive by the CSAC Institute for Excellence in County Government.
 

Assistant Sheriff Thomas Chalk - Support Services

Assistant Sheriff Thomas Chalk

Assistant Sheriff Chalk joined the Office of the Sheriff in 1998.  As a Deputy Sheriff, he was assigned to Detention, Transportation, County Patrol, Contract City Patrol, and Department Training Coordinator.  In 2006, he was promoted to Sergeant and served as a Patrol Supervisor, Police Academy Coordinator, and Assistant Facility Commander of the West County Detention Facility.  Assistant Sheriff Chalk was promoted to Lieutenant in 2010 and held the assignments of Watch Commander, Martinez Detention Facility Commander, and Valley Station Commander.  In 2012 he was promoted to Captain, where he served as the West County Detention Division Commander and Investigation Division Commander.

In January of 2020, Assistant Sheriff Chalk was appointed to his current rank and is assigned to the Support Services Bureau, which includes Emergency Services, Forensic Services, Coroner, and Technical Services Divisions.

Assistant Sheriff Chalk's formal education includes a Bachelor of Science Degree in Criminal Justice and a Master of Arts Degree in Organizational Leadership.  He is also a graduate of the F.B.I. National Academy and the California P.O.S.T. Command College.
 
 

Assistant Sheriff Steve Simpkins - Custody Services

Assistant Sheriff Steve Simpkins

Assistant Sheriff Steve Simpkins has been with the Office of the Sheriff since 1994.  As a Deputy Sheriff, he worked at the Martinez Detention Facility (MDF), County Patrol and the contract city of San Ramon.  Assistant Sheriff Simpkins was promoted to Sergeant in 2001 and worked at the MDF, County Patrol, and as the detective sergeant for the contract city of Orinda.  Assistant Sheriff Simpkins was promoted to Lieutenant in 2005 and served as the MDF Facility Commander, West County Detention Facility Commander and as a Watch Commander.  In July of 2010, Assistant Sheriff Simpkins was selected to be the Chief of Police for the Town of Danville and held that position until July of 2017; promoting to Captain in 2014.  As a Captain, he also worked in the Coroner’s Division and the Martinez Detention Division.  Prior to promotion to Assistant Sheriff, he served as the Interim Police Chief in Kensington.  

Assistant Sheriff Simpkins is a graduate of the FBI National Academy, Session #246 and POST Command College, Class #59.  His formal education includes a MA in Administrative Leadership from the University of Oklahoma, a BS in Organizational Leadership from Chapman University and an AS in Criminal Justice from Solano College.
 
 

Assistant Sheriff Mark Williams

Assistant Sheriff Mark Williams

Assistant Sheriff Mark Williams has over 25 years of law enforcement experience. He began his career with the Contra Costa County Office of the Sheriff as a Reserve Deputy Sheriff in 1991. During his law enforcement career, he has held a variety of assignments.

As a Deputy, Assistant Sheriff Williams worked in the Custody Services Bureau, County Patrol, and the contract City of San Ramon Police Department. He was a Field Training Officer, Traffic Officer, and served on the Sheriff’s S.W.A.T. Team. In 2001, he was promoted to the rank of Sergeant where he supervised in the Custody Services Bureau and Patrol Division before being assigned to the Internal Affairs Unit. As a Sergeant, he was also assigned to the Sheriff’s S.W.A.T. Team as an Assistant Team Leader for the Designated Marksman Team.

In 2006, Assistant Sheriff Williams was promoted to the rank of Lieutenant. He was assigned to the Field Operations Bureau where he held assignments as the Commander of the Marine Services/Air Support Unit, Administrative Lieutenant with the Town of Danville Police Department, and Bay Station Area Commander in Richmond. In June of 2011, he was promoted to the rank of Captain and remained in the Field Operations Bureau where he was assigned as the Patrol Division Commander.

In January of 2013, Assistant Sheriff Williams was appointed to his current rank and was assigned to oversee the Field Operations Bureau which includes the Patrol, Special Operations, and Investigation Divisions. In January of 2016, Assistant Sheriff Williams was assigned to oversee the Support Services Bureau which includes the Technical Services, Emergency Services, Coroner’s, and Forensic Services Divisions. In March of 2018, Assistant Sheriff Williams was assigned to oversee the Administrative Services Bureau which includes Capital and Special projects, the Personnel and Finance, Professional Standards, and Training Divisions.  Assistant Sheriff Williams is a graduate of Saint Mary’s College of California where he obtained a Bachelor of Arts Degree in Management. He is also a graduate of the California P.O.S.T. Command College.