Southern California faces a paradox: a persistent shortage of developable land alongside thousands of parcels shaped by more than a century of oil and gas production.
In many neighborhoods, legacy wells sit beneath homes, shops, and vacant lots, invisible on the surface but still influencing investment decisions, zoning reviews and environmental due diligence.
Too often, decisions about these parcels are slowed, not by confirmed risk, but by uncertainty. Fragmented records, incomplete historical context and datasets that were never designed to work together drive this uncertainty. When parcel boundaries, ownership, zoning and well records live in separate silos, even experienced stakeholders struggle to form a clear picture of site conditions.
The question is not what should be done with these parcels, but how they can be evaluated more clearly.
Much of the conversation around legacy oil infrastructure focuses on outcomes: whether a site should be redeveloped, remediated further, preserved or avoided altogether. Less attention is paid to the decision-making process that leads to those conclusions. Without a parcel-level spatial framework, risk is often assumed rather than measured. The result is not necessarily bad decisions, but slower, more cautious ones shaped by uncertainty rather than evidence.
Parcel-level integration fundamentally changes how legacy oil sites can be evaluated. Integrating tax parcels, ownership, structures, zoning and geocoding into a single, spatially consistent framework better reflects how real estate decisions are actually made.
When historical well data is layered onto that foundation, additional clarity emerges. CalGEM’s oil and gas well records provide detailed information on well location, status (active, idle or plugged) and owner/operator history. Viewed as standalone records, these datasets can be difficult to interpret. Spatially linked to parcels, they become far more informative.
Multiple data points needed
In our recent analysis of Signal Hill, a parcel-by-parcel approach surfaced details that were not visible in field-level summaries. The analysis identified clusters of parcels with consistent well status, compatible zoning, shared ownership or operator history, and common historical context. These findings do not dictate outcomes, but they materially improve how redevelopment options are evaluated.
Modern datasets rarely tell the full story on their own. Historical sources – including Sanborn Fire Insurance Maps, aerial imagery and city directories – provide essential context for understanding how today’s parcels came to be configured as they are.
Mid-century Sanborn maps often show above-ground storage tanks and supporting infrastructure adjacent to well sites, while city directories document nearby oil-field offices and service businesses. When aligned with modern parcel and well data, these materials help explain inconsistencies in records and illuminate long-forgotten site conditions.
Historical context does not replace modern data; it completes it.
Improved spatial clarity benefits every participant in the decision process. Developers gain a more accurate understanding of site conditions before committing capital. Regulators and planners can differentiate between materially different scenarios rather than applying broad assumptions. Lenders, insurers and advisers can evaluate risk with greater precision. A recent parcel-level analysis of Signal Hill illustrates how these conditions emerge across legacy oil fields when modern and historical data are evaluated together.
Legacy oil wells will continue to shape land-use decisions in Southern California, whether or not they are visible on the surface. The challenge is not their existence but how clearly they are evaluated
Richard W. White works in research and development focused on environmental due diligence at LightBox.
