This project investigates the historical ecology of the San Francisquito Creek watershed and reconstructs a bird’s eye view the landscape as it may have looked before the area was settled by Europeans (circa late 1700s). The purpose of the study is to provide information for future restoration discussions, to improve our understanding of what the area looked like, and how the ecosystem functioned prior to major human settlement. The primary outcome of our study is a landscape reconstruction - a visual synthesis of our best understanding of the historical landscape drawn from historical evidence, expert advice, and GIS analysis. The precise extents of redwoods, oaks, and other vegetation classes are exceedingly difficult to determine. The maps here show a “best informed guess” estimate of the extent, size, and density of these vegetation classes based on environmental suitability modeling informed by historical assumptions (described on the far right). Further research is necessary to validate the model assumptions, make informed adjustments to the extents of each vegetation class, and refine the visual depiction of historical conditions in specific areas of interest.

Our analysis focused on describing the historical hydrologic and topographic conditions and the extent, size, and density of six major vegetation types (redwood forest, oak woodland and savannah, riparian forest, grassland, chaparral and marshland) common in the Santa Cruz Mountains. While we have detailed survey data prior to the dam construction that describes the hydrology and topography of the study area, our knowledge of vegetation is mostly based on written accounts and is spatially imprecise. 

GIS suitability analysis is a predictive technique that balances multiple and diverse criteria to create suitability “rules” for land cover classes. In an iterative process, rules are weighted against one another to produce a series of suitability surfaces that define the probability of occurrence of each vegetation type, for example. Suitability rules are often based on deductive physical properties (e.g. water flows downhill), but can be derived from vague or qualitative statements (e.g. “the hillsides were covered with redwoods”) or partially quantifiable data (e.g. “redwoods most often occur on north-facing slopes”). This allows the analysis to make use of knowledge from diverse experts and to provide feedback on results at several stages. This iterative process ideally results in a realistic predictive map as experts have several opportunities to reject unrealistic options. However, caution must always be used in interpreting such maps as they are a “best informed guess” with considerable uncertainty.

We developed an initial suitability model based on a regional analysis of environmental conditions (e.g. slope, aspect, elevation) for each vegetation class in present-day sites on the eastern slopes of the Santa Cruz Mountains. These rules were then applied to historical topographical conditions as derived from a detailed survey of the study site in and around San Francisquito Creek ahead of the Searsville Dam construction (1891) to identify likely areas for each vegetation class. Our analysis was done at a high enough resolution (1m pixel grid) to produce large scale maps of the area.

Next, we critically analyzed the best available historical information (e.g. explorer accounts, secondary sources, maps, photos, etc.) to improve the initial raw suitability analysis. To guide this process, we developed a set of “historical assumptions” through a series of workshops with participants from Jasper Ridge, Stanford, and the wider public in botany, ecology, hydrology, geography and archealogy. The workshops and a digital survey culminated in a set of historical assumptions agreed upon by the participants and a coarse estimate of the historical species composition of each vegetation class.

Weighted suitability surfaces were calculated and compared by balancing the relative importance of factors such as climate and land-use practices. Each result was then evaluated against our historical assumptions and knowledge of the local ecology, and improved iteratively until the final map met both the “rules” for environmental conditions and the historical assumptions developed by the experts. The final result was a possible four separate layers for each vegetation class (extent, size, color and density). Micro adjustments to vegetation extents and densities were made manually to improve the reliability in some areas, remove unintentional artifacts, and ease transitions between vegetation classes. 

Final renderings were created using VUE by e-on software, a natural landscape 3D rendering program with a procedural tree species library. We were able to acquire digital models for relevant tree species (e.g. live oak, coast redwood) that follow detailed rules for tree form to produce a realistic landscape rendering where no two trees are identical. As a 3D model, the landscape could then be rendered from any angle and at a very high resolution (the tree models include individual leaves, for example).

Once complete, the rendering provided a hypothetical view into the past but comparing this view to present-day maps or air photos was more challenging than we anticipated. Comparing historic to present was enough of a visual disjuncture that viewers seemed to evaluate the reliability of the historical rendering in broad terms rather than focusing on specific areas of interest. We ultimately decided to develop a 3D model of the present-day conditions in a similar fashion so that viewers could directly compare the changes. The present-day model was developing using current GIS data, aerial imagery and photographs.

For our analysis, we collected historical content in the form of written accounts, surveys and photography.

Explorer Accounts, late 1700s

The earliest written descriptions of landscape in the local area come from Spanish expeditions (1769, 1770, 1772, 1774, 1775, and 1776). None of the Spanish explorers traveled precisely through the study area although they did come tantalizingly close. On the 1769 expedition, Father Juan Crespi when arriving further north along San Francisquito Creek mentioned seeing what appear to be pines or “savins” (his word for redwoods) in the distance, as does geographer Miguel Costanso. Both men also take note of the extensive oaks in the area. In 1774, Captain Fernando Rivera also stopped at San Francisquito Creek, describing it as rising “from a small mountain range, covered with the [red-]wood,” with many “acorn-bearing live-oaks” nearby. Father Francisco Palou also wrote about camping at San Francisquito Creek, and noted it was lined with cottonwoods, willows, sycamores, laurels, brambles, additional species he could not identify and clumps of “very tall trees of a red-wood sort, and about a hundred paces farther down, another very large one of the same red-wood, which can be seen more than a league (2.6 miles) before crossing the creek and from afar looks like a tower.” In 1776, Father Pedro Font wrote about crossing San Francisquito Creek, “where a spruce-tree [some of the Spanish referred to the redwoods as spruces or larches] upon the bank was seen which, when measured by the graphometer, appeared to be fifty yards in height, and was five and a half [yards] in circumference at its foot.” 

Rancho Maps, early 1800s

The earliest maps of the vicinity were diseňos drawn for Mexican land grants in the area and covered Rancho El Corte de Madera, Rancho de las Pulgas and Rancho Caňada de Reymundo. These show large individual redwoods and oaks as survey markers, which persist on later maps. Such notations indicate the presence of redwoods but say little about their general prevalence and may even suggest that they were relatively rare.

Dam Site Photography, 1890

Looking upstream from the future dam site, you can see a flat-bottomed valley devoid of vegetation or stumps and few trees on surrounding hillsides. The photo was taken after nearly all harvestable timber was removed from the region. Image courtesy of Stanford Special Collections

Looking (apparently) downstream towards the construction site at the dam, you can see a dry hillside mostly devoid of vegetation, with a few small chaparral-type bushes (perhaps California Sagebrush or Chamise). The photo shows no evidence of trees below the current water level of Searsville Reservoir. Image courtesy of Stanford Special Collections

Dam Site Survey, 1891


This pre-dam topographic survey map details water courses, elevation contours, and some built structures in the vicinity. An area of swamp is indicated in the area of Lloyd’s Pond or Upper Marsh. The confluence area where Corte Madera Creek and Alambique Creek join shows little evidence of marshland vegetation.

Dennis Martin Creek Photograph, c. 1900




This photo depicts a residence and operational structures of E.F. Preston’s winery along Dennis Martin Creek. The winery produced 175,000 gallons of wine in 1887. Grassland and chaparral hillsides have replaced a prior landscape, but there is little evidence that redwoods were prevalent here recently.

Redwood Forest

Explorer descriptions of the region frequently noted the size, quality, and abundance of redwoods in the Santa Cruz Mountains. Their journals also indicate there were several isolated stands, including below the site of the present-day dam along San Francisquito Creek extending down to the future site of Palo Alto. Later Rancho maps used redwoods as survey markers, indicating their presence but not their prevalence.

The transition from redwood-dominant forest to oak-chaparral-grassland vegetation types happened within the study area, although it is unclear where. There is some evidence that historic climate conditions were slightly cooler and wetter than today, with increased fogginess supportive of redwood growth. 

Logging in the area began as early as 1777 with the establishment of Santa Clara Mission near San Jose and continued through the Mexican Period. Eventually, with the growth of San Francisco during the period of 1840s-1870s, logging all but eliminated redwoods from the study area and in much of the Santa Cruz Mountains. 

Redwoods and other conifers present in the area today are second-growth stands less than 150 years old found near streams, on private property, and in the upper stretches of Dennis Martin Creek. A few isolated redwood trees are present below the dam.
A photograph looking up Dennis Martin Creek around 1900 shows no apparent evidence of redwood stumps, and mostly barren steep hillsides that have since been replaced by oak woodland.

Oak Woodland and Savanna

Due to their high nutritional value and abundance, acorns of the tanbark, blue, live and valley oak were a significant source of food for Native inhabitants of this area. Native grasses and other seed bearing plants were also important. Their land management practices would have been oriented toward supporting nut and seed production. Most significantly, these included burning woodland undergrowth to thin the woodland and understory shrubs, improve visibility, enable access, and to promote seedling growth.

With the arrival of the missions, oaks were a significant source of timber and were heavily logged throughout the 1800s, although less so than redwoods. The introduction of substantial grazing would have suppressed oak regeneration in the grassland communities and adjacent areas, sustaining the open oak savanna that had been previously maintained by fire. 

In the last century with the absence of fire, logging, and (more recently) grazing. oaks have regrown to cover historical extents in the Jasper Ridge Biological Preserve, residential areas, and in areas where there were previously redwood stands. Although it is difficult to determine the exact extent of oaks historically, it is assumed that they would have required similar site conditions as today’s forest. 

However, oak woodlands today are likely more homogenous with denser undergrowth than their historical structure. The historic woodlands and savanna likely had a more open canopy and varied tree ages, notably with older, larger trees. In open savanna areas, there were likely fewer trees overall as secondary shrub and seedling recruitment have filled out the prairie in the last century.

Riparian Forest

A detailed topographic survey of the study area performed before dam construction began in 1891 reveals some clues that the historical streams were mostly free-flowing with moderate gradient profiles.

Sediment deposition over centuries led to the establishment of a flat-bottomed canyon under the area of the current lake extending up Corte Madera Creek. These meandering channels would have likely supported a wide riparian zone along the current and historical stream tributaries.

Further upstream, Sausal Creek likely supported a broad riparian forest in flatter areas along the San Andreas Fault above where it joins the steeper Dennis Martin channel. Dennis Martin Creek, with its steep profile, would have had a narrow riparian belt but this would have spread out as the streams joined Alambique Creek.

Substantial erosion as a result of deforestation upstream and subsequent sedimentation since the dam construction has lowered all of the stream water profiles and promoted riparian and marshland vegetation, particularly along Alambique Creek and its confluence with Corte Madera.

Historically, the riparian forest structure would have been more varied with a more open canopy due to beaver activity and fire. The areas adjacent to streams were almost certainly logged over and used for irrigation and grazing in the 1800s. The recovered riparian forest is younger and dominated by moisture-tolerant species than it was historically.

Chaparral

In dense, woody stands, chaparral was generally undesirable for Native inhabitants who burned mature stands regularly to encourage herbs and forbs, improve mobility and support hunting. As chaparral is extremely flammable, these fires may have been difficult to control and could have charred broad areas before recovering from deep roots within 5-10 years. Areas that were burned repeatedly in short cycles could have been converted to grasslands. 

Livestock grazing introduced in the 1800s would have contributed to keeping chaparral at bay on the edges of pastureland. Subsequently, chaparral would have been painstakingly removed to allow for cultivation of grain, vineyards and orchards. Chaparral and its roots could be sold for wood and charcoal, especially during the late 19th century boom. 

In the last century with fire suppression and the reduction of grazing, chaparral has recovered in areas that were grazed or logged. Some areas may have been chaparral continuously since the 1700s as large uninhabitable areas are still noted on Stanford property in the late 1800s. 

With such a varied history, it is difficult to assess the exact extent of historical chaparral at any given time compared to today, we can only presume similar site conditions and distribution.

Grassland

Historically, native grasslands were abundant in the study area, maintained through frequent burning from lightning- and human-caused fires and grazing by natural herbivores. 

Native Americans burned grasslands and chaparral to enable mobility, encourage grass and seed production, drive game, and promote visibility. Frequent burning could have limited the extent of sagebrush and chaparral. 

Significant grazing was introduced with ranching during the Mission and Mexican periods and later. Grazing suppressed chaparral and oak regrowth and favored the non-native grasses introduced by the Spanish. The area was also cultivated as grain fields, vineyards, and orchards, which were developed on existing grassland or cleared chaparral. In combination with the significant logging during the 1800s, by the time of the dam construction the area was mostly devoid of trees. 

Livestock were active in Jasper Ridge until 1960 and in surrounding areas for longer. In the last half-century, especially with fire-suppression and the elimination of logging and grazing, oak woodlands, savanna, and chaparral have reclaimed significant parts of the landscape, reducing the extent of grasslands. 

Areas adjacent to Searsville Lake and the tributaries of San Francisquito Creek have substantially recovered as dense wooded areas. Although non-native European grasses have replaced most of the native grasses, some areas still persist, principally on the high serpentine ridge to the east of the study area.

Marshland

With respect to ecological changes in the study area over the last two centuries, the growth of ponds and marshland is perhaps the most apparent (aside from the Reservoir itself). Substantial sedimentation from Sausal, Dennis Martin, and Alambique Creeks above Searsville Lake has significantly modified the topography, transforming their stream profiles from moderate to very low. Their confluence now forms a wide, flat, marshy area surrounded by riparian forest.

The current wetland vegetation supports several aquatic and semi-aquatic species in a broad zone extending up to and beyond Portola Road to Upper Marsh. With strong seasonal stream flow patterns, these areas are typically dry during the summer and fall and moist during the winter and spring.

From historical maps we know of two ponds or marshes in the area, the largest being approximately the area west of Portola Road denoted as “Lloyd’s Pond.” The marsh was drained by Alambique Creek and was adjacent to the town of Searsville, established in the 1860s but ultimately abandoned when the reservoir was filled.

Few if no other areas would have likely supported marshland communities, even at the major confluence of Alambique and Corte Madera Creeks at the end of the current reservoir.

Over two centuries, this landscape has been transformed many times over through resource extraction, destructive land use, residential development, hydrologic manipulation, and preservation. The 1891 dam had the most profound impact, creating the reservoir that has held back a century’s worth of sediment and debris (see below), adding significant area to the aquatic and semi-aquatic habitat (see below). In other areas, land use and climate changes have likely reduced the area of grassland, eliminated lowland redwoods, and expanded the presence of chaparral and oak.