Maps have come a long way. Historic maps of the Slough were drawn by hand. They provide a rare snapshot into the Slough’s past and how humans have altered the landscape over time.

Geographic information systems or GIS emerged in the 1970 and 80s. GIS changed forever the way maps were created and analyzed. GIS is a tool that manages, analyzes, and models data from our environment so that we can make decisions based on that information to better study changes over time, conserve and restore important resources, and protect biodiversity into the future.

Find out more about Historical Ecology Tools utilized by our Stewardship Programs.

Past, Present, and Future

Empire Gun Club

Geographic Information Systems technology is helping ESNERR understand the ecological history of the Slough. California’s coastal wetlands have undergone dramatic hydrologic modifications and land use changes over the years. At Elkhorn Slough, marshlands were diked and drained and converted to agriculture. In 1947, an artificial opening to the Monterey Bay was constructed that exposed the Slough to increased tidal exchange.

By digitizing, rectifying, assembling, and analyzing a chronological sequence of historical maps and aerial photographs, we are beginning to quantify patterns of change to the Slough’s wetland habitats and correlate them with historic events.

A specific focus for this research program is to measure rates of tidal erosion, changes in tidal creek morphology, and loss of vegetated salt marsh. We hope to determine whether these trends are accelerating or – hopefully – approaching a new equilibrium.

Map of Habitat Types

Map of habitat types

GIS helps us understand not only Elkhorn Slough’s past, but also its present. Using the combination of sophisticated digital image analysis and old-fashioned (GPS-assisted) field survey work, we produce highly accurate habitat and vegetation maps and perform landscape and connectivity analysis.

Accurate maps of present conditions and an understanding of historic changes are powerful tools for informed stewardship and conservation. Perhaps the most important role for our GIS-based research is for the future: building an accurate baseline to monitor future habitat changes and to guide restoration.

Spatial Data

The Elkhorn Slough NERR, in cooperation with the Elkhorn Slough Foundation, maintains an extensive library of digital aerial imagery of the Slough’s wetlands and adjoining upland areas dating from the 1930s through to the present. The California Department of Fish and Wildlife augments the collection with aerial surveys flown every spring and fall.

The Reserve is also assembling a collection of historic and contemporary maps and a variety of other types of raster and vector spatial data including elevation models and vegetation, land use, and soils coverages.

Download ArcGIS Shapefiles
Click below to download shapefiles covering the Elkhorn Slough watershed that can be viewed and manipulated using ESRI’s ArcGIS software.  The files are in the following coordinate system:  UTM Zone 10 WGS84.

If you do not use ArcView, ArcGIS, or Arc/Info, you can obtain ESRI’s ArcGIS Explorer Desktop program to view and query data layers. Although you cannot add or modify graphics or tables, you can perform many of the viewing functions that ArcView allows you to do. ArcGIS Explorer can be downloaded for free from:

File Description
15.7 MB
2009 Semi-automated habitat classification for Elkhorn Slough.  Habitat classes are distinguished according to the theme table field “CODE_DESC”.
2.15 MB
2002 Habitat classification for the Elkhorn Slough watershed. Habitat classes are distinguished according to the theme table field “Class”.
55 K
Open water, including Monterey Bay, the Elkhorn Slough main channel, and the Moro Cojo Slough channel.
239 K
Outline of Elkhorn Slough’s tidal wetlands.
40 K
Streams in the Elkhorn Slough watershed.
60 K
Boundary of the Elkhorn Slough watershed and its sub-watersheds.
79 K
The Elkhorn Slough watershed’s protected lands. Ownership is specified in the “Protected” theme table field.
63 K
Roads in the Elkhorn Slough region. Roads can be labeled with names in the “Name” field.
28 K
The coastal zone boundary in the vicinity of Elkhorn Slough.