This post originally appeared on Burt M. Polson's Real Estate Journal and is republished with permission. Find out how to syndicate your content with theBrokerList.


The Napa earthquake of 2014 likely affected the value of several homes close to the fault with several owners finding it may be difficult to sell at some time in the future.

In part one, we reviewed the new Alquist-Priolo earthquake fault zone map which now confirms the location of the fault running from north Vallejo, through American Canyon up through north-west Napa.

When examining a map, you will find a yellow-shaded area following the actual fault and averages a quarter of a mile in width.  This area is where development could be restricted.

The Cuttings Wharf map includes the area of Highway 29 through American Canyon. There you will find many undeveloped commercial parcels that unfortunately are within the earthquake fault zone.

One project currently underway is the Village at Vintage Ranch, a 159-unit apartment development in American Canyon. Located on the northeast corner of Highway 29 and American Canyon Road the West Napa Fault runs directly through the project.

As part of a project’s entitlements, the developer is required to identify the exact location of the fault. Locating a fault is usually accomplished by hiring a geologist to perform reconnaissance of the site by first digging several deep trenches perpendicular to the probable location.

The geologist can then determine the location and direction of the fault by examining the walls of the trench. They also use trenching which may have occurred on other adjacent properties thereby mapping out the fault. The Walgreens site to the south had trenching done before development which the geologist can use to confirm the direction of the fault.

The geologist identified the location of the fault within the Village at Vintage Ranch and recommended no inhabited structure within 50 feet on each side of the fault. The requirement essentially bisected the development into two areas with the 100 foot section being used for parking and greenbelt.

The real test of value lies in a site with development potential.  The Village at Vintage Ranch site is zoned cluster residential allowing for 12 to 18 units per acre. At 11.5 acres the possibility exists for 138 to 207 units. This project is entitled for 159 units and falls within the range, but there was potential for more.

Many factors go in to determine the potential number of units allowed on a site including parking, streets, landscaping, easements, drainage, topography, and setbacks with the fault line playing a significant role.

Other sites in American Canyon along Highway 29 are within the fault zone and may even have the fault run through it. The development potential of a parcel could be affected so much so that the size of a structure may be drastically reduced or even found to be undevelopable.

In either case, the potential for the number of units or size of the building correlates to the value of the parcel to a developer.

Burt M. Polson, CCIM, is an active commercial real estate broker. Reach him at 707-254-8000, or [email protected] Sign up for his email newsletter at

Do NOT follow this link or you will be banned from the site!