Contra Costa County Historical Landmarks Advisory Committee (HLAC)
Staff Report for May 8, 2025, Meeting
1. Call to Order
2. Public Comment:
3. Acceptance of Summary Minutes for February 13, 2025, Meeting
4. Discussion Items:
A. County File #CDCV25-00028: Request for Historic Nomination to the County HRI for a residential house building located at 205 Lake Drive in Kensington to qualify for a Mills Act contract.
o A Historical Resources Evaluation (HRE) has been prepared by Pierluigi Serraino, Ph.D., FAIA to evaluate the potential resources eligibility to be nominated to the HRI, and is attached to this staff report.
o The HRE states the building is eligible under criterion 2: Associated with the lives of persons important to local, California or national history. Harold L. Thiederman is recognized as an influential 20th century architect for the Bay Area. Thiederman designed the Alumni Hall at UC Berkeley, as well as the Kaiser Clinics in Napa, Walnut Creek, and Redwood City, and later on the Kaiser Foundation Hospital in Hayward, and the Kaiser Medical Center in Terra Linda.
o The HRE states the building is also eligible under criterion 3: Embodies the distinctive characteristics of a type, period, region or method of construction or represents the work of a master or possesses high artistic values. Its mid-century modern architecture remains intact. Built in 1949, Thiederman purchased it in 1962, and designed two out of three subsequent additions while living there.
o The HRE concludes with an Integrity Analysis using the seven aspects of integrity (location, design, setting, materials, workmanship, feeling, and association) as established by the National Parks Service.
o Staff recommends that this item be continued until further analysis is provided on the integrity of the historical resource, and a draft Mills Act 10-year Rehab Plan is prepared showing the intended work necessary to rehabilitee the building.
B. County File#CDCV25-00032: Request to determine if a residential house building located at 1850 Alameda Diablo in the Diablo Historic District has maintained its historic integrity to qualify for a Mills Act contract.
o A Historical Resources Evaluation (HRE) has been prepared by Mark Hulbert, qualified Preservation Architect, to assess if the proposed Mills Act 10-year Rehab Plan meets the U.S. Secretary of the Interior’s Standards (SOIS) for the Treatment of Historic Properties, specifically, the Standards for Rehabilitation, and is attached to this staff report.
o Originally built in 1917, during the period of significance for the Diablo Historic District.
o Additions have taken place since its original construction.
o The HRE includes a proposed rehab plan and an SOIS analysis.
o Staff recommends that this item be continued until an Integrity Analysis be provided, as well as a revised rehab plan that specifies when the work would take place over the course of 10-years and a revised SOIS that expands on number 6, providing specific material choices.
C. Consider Recommending to the Board of Supervisors Support the Contra Costa County Historical Society
o The Contra Costa County Historical Society (CCCHS) is requesting an increased stipend from the Board of Supervisors to cover inflation costs and is also requesting a new building of operation.
o As members of the CCCHS, the HLAC wish to extend their support of the CCCHS.
o At the last meeting, the HLAC moved to request staff report to the Board that the HLAC recommends to them to support the Contra Costa County Historical Society in receiving an increased stipend from the County and be located in the County owned building.
o HLAC staff will present what options are available to the HLAC based on this motion.
D. Attending Transportation, Water & Infrastructure Committee (TWIC)
o The HLAC presented to the Board of Supervisors on August 15, 2023, and recommended that the County adopt a Historic Preservation Ordinance, and provided the Board with a draft ordinance they had prepared.
o The Board considered the recommendations of the HLAC, and referred the matter to the Transportation, Water and Infrastructure Committee (TWIC), and directed Department of Conservation and Development (DCD) staff to provide analysis on this item for TWIC’s consideration.
o This meeting took place on Monday, February 24th at 1:00PM.
o TWIC accepted the report and directed DCD staff to return at a future meeting with a report outlining a range of ordinance options, including input from other counties, potential cost recovery mechanisms, and how the ordinance would apply (e.g., to designated or contributing structures only). The Committee expressed general support for historic preservation but emphasized the need to balance these efforts with property owner rights. Concerns were raised regarding potential legal implications, staffing and cost impacts, and how such an ordinance would differ from or expand upon existing CEQA protections.
o Staff will provide the HLAC with a status update of this item.
E. Status of the Contra Costa County 2045 General Plan
o The new General Plan was adopted in November of 2024.
o With its adoption, the new goals, policies and action items are now effective.
o There are action items within Chapter 7 of the new General Plan that are of interest to the HLAC: COS-A10.1, 10.2, 10.3, and 10.4.
o HLAC staff will continue to update the HLAC on the progress of these action items.
F. Delta National Heritage Area (NHA) Management Plan Update - Carol Jensen
o HLAC Chair, Carol Jensen, is a member of the NHA Advisory Committee.
o NHA webpage: Sacramento-San Joaquin Delta National Heritage Area - Delta Protection Commission (ca.gov) <http://delta.ca.gov/nha/>
o This Discussion item provides Chair Carol Jensen the opportunity to share the current progress of this with the HLAC.
G. Properties of Interest to the HLAC:
Properties within unincorporated County with that are of historical interest to the HLAC.
§ Contributor property to the Diablo Historic District - 1699 Alameda Diablo, Diablo
o In-progress 2-lot subdivision (County File #CDMS24-00013) is currently being prepared to be heard by the Zoning Administrator, tentatively June 2nd or 16th.
§ TUGS restaurant - 6201 Bethel Island Road, Bethel Island
o No change in status - pending response to Building’s comments.
§ Byron Hot Springs - 5400 Byron Hot Springs Road, Byron
o No change in status - pending response to Building’s comments.
§ No Permit Activity:
o Nail Ranch - 3890 and 3900 Sellers Avenue, Brentwood
o Diablo Country Club - 1700 Club House Road, Diablo
o Bethel Island Fire Station - 3045 Ranch Lane, Bethel Island
o Eugene A. Bridgford house - 4090 Gateway Road, Bethel Island
o Knightsen Saloon - 3055 Knightsen Ave, Knightsen
5. Committee Member’s Comments
o HLAC members provide suggestions for items to be included on the next agenda.
6. Next Agenda Discussion: Thursday, August 8, 2025, at 2:30 PM.
Attachments:
1. Summary Minutes for February 13, 2025, Meeting
2. Historical Resources Evaluation report for item 4A
3. Historical Resources Evaluation report for item 4B