Glen Canyon Park is a city park in San Francisco

San Francisco, California

San Francisco , officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.15 million people which includes San Jose and Oakland...

, California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. It occupies about 70 acres (28.3 ha) along a deep canyon

Canyon

A canyon or gorge is a deep ravine between cliffs often carved from the landscape by a river. Rivers have a natural tendency to reach a baseline elevation, which is the same elevation as the body of water it will eventually drain into. This forms a canyon. Most canyons were formed by a process of...

 adjacent to the Glen Park

Glen Park, San Francisco, California

Glen Park is a small neighborhood in San Francisco, California, named for the adjacent Glen Canyon Park.-Location:It is at the southern edge of the hills in the interior of the city, to the south of Diamond Heights and Noe Valley, west of Bernal Heights, and east of Glen Canyon Park...

, Diamond Heights, and Miraloma Park neighborhoods

Neighborhoods in San Francisco, California

San Francisco has both major, well-known neighborhoods and districts as well as smaller, specific subsections and developments. While there is considerable fluidity among the sources, one guidebook identifies five major districts, corresponding to the four quadrants plus a south central district...

. O’Shaughnessy Hollow is a rugged, undeveloped 3.6 acres (1.5 ha) tract of parkland that lies immediately to the west, and may be considered as an extension of Glen Canyon Park.

The park and hollow offer an experience of San Francisco's diverse terrains as they appeared before the intense development of the region in the late 19th and the 20th Centuries. The park incorporates free-flowing Islais Creek

Islais Creek

Islais Creek or Islais Creek Channel is a small creek in San Francisco, California...

 and the associated riparian

Riparian zone

A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the fifteen terrestrial biomes of the earth. Plant habitats and communities along the river margins and banks are called riparian vegetation, characterized by...

 habitat, an extensive grassland with adjoining trees that supports breeding pairs of red-tailed hawks and great horned owls, striking rock outcrops, and arid patches covered by "coastal scrub

Coastal sage scrub

Coastal sage scrub is a low scrubland plant community found in the California chaparral and woodlands ecoregion of coastal California and northern Baja California. It is characterized by low-growing aromatic, and drought-deciduous shrubs adapted to the semi-arid Mediterranean climate of the...

" plant communities. In all, about 63 acres (25.5 ha) of the park and hollow are designated as undeveloped Natural Area. Elevations in Glen Canyon Park range from approximately 225 feet (69 m) above sea level at the south end of the park to 575 feet (175 m) above sea level at the north end and along the east rim of the canyon; the walls of the canyon are extremely steep, with many slopes approaching a length-to-height ratio of 1:1 (100 percent).

Formal recreational facilities in Glen Canyon Park are mostly located at its southern end (see the aerial photograph). These facilities include a community recreation center, ball fields and tennis courts, playgrounds, and a ropes course. The park is also well-used by local rock climbers, who consider it one of the best "bouldering" sites near San Francisco. An additional building about halfway up the canyon near Islais Creek serves the Silver Tree Day Camp and the Glenridge Cooperative Nursery School.

The park is easily entered at its southeastern corner (end of Bosworth Street). Somewhat further north, there is a wooden stairway leading down into the park (the Sussex Street entrance). There are also trails leading into the park from the Diamond Heights Shopping Center. Of one of these, Joseph Stubbs has written "It is a dramatic, sudden revelation of the park interior from high up which is simply stunning. It occurs midsection of the park behind Diamond Heights Shopping Center and George Christopher Playground."

Islais Creek

A branch of Islais Creek

Islais Creek

Islais Creek or Islais Creek Channel is a small creek in San Francisco, California...

 (named after the wild cherry islay

Prunus ilicifolia

Prunus ilicifolia is an evergreen shrub to tree, producing edible cherries, with shiny and spiny toothed leaves similar in appearance to holly...

) originates in the canyon. It is the largest remaining creek in San Francisco with public access. The bottom of the canyon, where Islais Creek flows, is irregular but moderate in slope, dropping 350 feet (107 m) over a distance of about 1 mile (1.6 kilometer). The creek is presently surrounded by willow thickets. In earlier times, the creek had an open water channel sustained by a much larger water flow, and was "more of a river than a creek". Urban development has reduced the watershed of Islais Creek by as much as 80 percent. At the southern end of the canyon, Islais Creek enters a culvert which carries it to its exit into San Francisco Bay.

Wildlife

The creek has a meager but year-round natural flow, and the water and resulting vegetation provide a habitat for animals, including skunks, opossums, raccoons, red-tailed hawks, red-shouldered hawks, great horned owls, coyotes, and the rare native San Francisco forktail damselfly, Ischnura gemina.

Geology and Rock Outcrops

The scenery of Glen Canyon Park is also distinguished by numerous large outcrops of rock. The most striking of these consist of reddish, layered "Franciscan

Franciscan Assemblage

The Franciscan Assemblage is a geological term for an accreted terrane of heterogeneous rocks found on and near the San Francisco Peninsula. It was named by geologist Andrew Lawson who also named the San Andreas Fault which bounds the Franciscan Assemblage....

" chert

Chert

Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...

. These outcrops have clearly visible banding (see photo) which is due to the different weathering of the layers.

The bedrock of the canyon is made up of rocks of the Marin Headlands terrane

Terrane

A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...

, which is a large packet of rock that extends diagonally from the Marin Headlands (just north of the Golden Gate

Golden Gate

The Golden Gate is the North American strait connecting San Francisco Bay to the Pacific Ocean. Since 1937 it has been spanned by the Golden Gate Bridge...

), through the Twin Peaks and Glen Canyon area, and on to the southeast. This terrane is from 100 to 200 million years old (i.e. the Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 and Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 periods). The bedrock of the lower slopes of the canyon - largely hidden under slope debris/ravine fill - is pillow lava

Pillow lava

Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...

 or greenstone; these erupted from fissures in the deep ocean floor when the terrane was located hundreds of miles southwest of its present location.

The upper slopes and cliffs are of layered chert

Chert

Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...

, which hardened into rock from the ooze of remains of countless radiolarian creatures that accumulated on top of the lava. The ooze was colored red by iron from hydrothermal springs

Hydrothermal circulation

Hydrothermal circulation in its most general sense is the circulation of hot water; 'hydros' in the Greek meaning water and 'thermos' meaning heat. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust...

. Both lava and chert were formed in the deep ocean near the equator, and were rafted northeast on the gradually-moving ocean floor toward California. Near shore, greywacke

Greywacke

Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...

 accumulated on the chert in some areas, including a small part of the southeast slope of Glen Canyon. Subduction

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 then squeezed the terrane against the continent, and it eventually became part of the Franciscan formation

Franciscan Assemblage

The Franciscan Assemblage is a geological term for an accreted terrane of heterogeneous rocks found on and near the San Francisco Peninsula. It was named by geologist Andrew Lawson who also named the San Andreas Fault which bounds the Franciscan Assemblage....

 that makes up much of coastal California. During subduction - 160 to 80 million years ago - and the subsequent uplift, the terrane was twisted, broken and disrupted, and the chert was deformed into the tight folds now visible in road cuts along O'Shaughnessy Boulevard (see photo).

Sutro's Gum Tree Ranch

The park's history commences with Adolph Sutro

Adolph Sutro

Adolph Heinrich Joseph Sutro was the 24th mayor of San Francisco, and second Jewish mayor, serving in that office from 1894 until 1896...

's purchase in the 1850s of 76 acres (307,561.4 m²) of the canyon, which he named "Gum Tree Ranch" after the blue gum eucalyptus

Eucalyptus globulus

The Tasmanian Blue Gum, Southern Blue Gum or Blue Gum, is an evergreen tree, one of the most widely cultivated trees native to Australia. They typically grow from 30 to 55 m tall. The tallest currently known specimen in Tasmania is 90.7 m tall...

 trees he had planted.
The first commercial manufacturing of dynamite

Dynamite

Dynamite is an explosive material based on nitroglycerin, initially using diatomaceous earth , or another absorbent substance such as powdered shells, clay, sawdust, or wood pulp. Dynamites using organic materials such as sawdust are less stable and such use has been generally discontinued...

 in the U.S. occurred in the canyon; on March 19, 1868, the Giant Powder Company began production at its first manufacturing plant, under exclusive license from Alfred Nobel

Alfred Nobel

Alfred Bernhard Nobel was a Swedish chemist, engineer, innovator, and armaments manufacturer. He is the inventor of dynamite. Nobel also owned Bofors, which he had redirected from its previous role as primarily an iron and steel producer to a major manufacturer of cannon and other armaments...

 to produce his new explosive in America. The plant was apparently located near the present recreation center, at the southern end of the park. The factory did not last long. On November 26, 1869, an explosion completely destroyed the entire facility, turning every one of the buildings on the place, and the surrounding fencing, into "hundreds of pieces", according to a newspaper account. Two people were killed, and nine injured; the plant was subsequently rebuilt in the sand dunes south of Golden Gate Park. The site of the plant has been designated as California Landmark 1002, although no marker has been placed on the site.

The Crocker era

In 1889, the Crocker Real Estate Company bought the canyon to develop a neighborhood that would attract homebuyers. As Jeanne Alexander has written,

A City Park

O'Shaughnessy Boulevard currently defines the western perimeter of Glen Canyon Park. This street was built in 1935 using roadcuts and filled slopes on the canyon's steep slopes, and was named after Michael O'Shaughnessy, who was for many years the Chief Engineer of the City. The recreation center at the south end of the park was built by the Works Progress Administration

Works Progress Administration

The Works Progress Administration was the largest and most ambitious New Deal agency, employing millions of unskilled workers to carry out public works projects, including the construction of public buildings and roads, and operated large arts, drama, media, and literacy projects...

 in 1937. An undeveloped, very steep area just west of O'Shaughnessy Boulevard was purchased by the City of San Francisco in the 1990s, and named O'Shaughnessy Hollow.

In 1958, the California State Highway Department proposed a plan to widen O'Shaughnessy Boulevard as part of a Crosstown Freeway. Some work was done at the southern end of the park, and homes and businesses were demolished along Bosworth Street to permit its widening. Further work ceased following opposition by several groups; the conflict over the freeway was among the earliest incidents in the Freeway and expressway revolts

Freeway and expressway revolts

Many freeway revolts took place in developed countries during the 1960s and 1970s, in response to plans for the construction of new freeways, a significant number of which were abandoned or significantly scaled back due to widespread public opposition; especially of those whose neighborhoods would...

 of the 1960s and 1970s.

Future Management of Glen Canyon Park

The city government of San Francisco mandated the development of management plans for all the "natural areas" under the city's control, and this process culminated in release of the Significant Natural Resources Areas Management Plan in February 2006. The plan favors the re-establishment of native species and species diversity in the city's parks. Some aspects of the plan have been controversial. For example, the plan envisions the removal of some large, mature trees (often eucalpytus, which was imported from Australia) to favor smaller native plants. The plan also includes new restrictions on recreational use of the park, such as the closure of some trails and of some areas for rock climbing, and prohibitions against unleashed dogs.

In Glen Canyon Park, about 20 mature eucalpytus trees were removed in 2004 as part of an effort to increase the diversity of species living along Islais Creek. The plan envisions the removal of an additional 120 trees (of the total of 6000 trees in the park) to further improve the creek, to increase the extent of the park's grasslands, and to promote forest understory plants. The plan also seeks to restore some open-water areas along the creek, which is presently nearly totally obscured by the willow thickets. The change in the creek would be established both by re-planting sections of the creek's banks with different plants and by the introduction of "scouring" structures.

Glen Canyon Park formerly supported populations of two rare species: the "vulnerable" San Francisco forktailed damselfly

Ischnura gemina

Ischnura gemina is a species of damselfly in the family Coenagrionidae. It is endemic to the United States.-Source:* Odonata Specialist Group 1996. . Downloaded on 9 August 2007....

 and the "endangered" Mission blue butterfly. The plan proposes changes in the management of the park that would promote self-sustaining populations of these insects. The damselfly population in the park was studied by John Hafernik and his colleagues in the 1980s prior to its local extinction; they re-introduced a population of these damselflies in 1996 that persisted for two seasons. The damselflies need open water habitat, which has proven difficult to maintain.

There has been a declining population of Mission blue butterflies at the nearly contiguous Twin Peaks

Twin Peaks, San Francisco, California

The Twin Peaks are two hills with an elevation of about near the geographic center of San Francisco, California. Except for Mount Davidson, they are the highest points in the city.-Location and climate:...

 Natural Area; while park employees logged about 150 butterflies in the 1980s, only four were found between 2001 and 2007. A reintroduction was done in April 2009. Reintroduction may also be possible in Glen Canyon Park. Here the main issue appears to be re-establishing the native plant "silver bush lupine

Lupinus albifrons

Lupinus albifrons, Silver lupine, white-leaf bush lupine, or evergreen lupine, is a species of lupine . It is native to California and Oregon, where it grows along the coast and in dry and open meadows, prairies and forest clearings...

", whose leaves are the larval food of these butterflies. A substantial fraction of Glen Canyon Park is now covered by non-native species including eucalyptus

Eucalyptus

Eucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia...

 forest (17 acres), French broom

French Broom

Genista monspessulana also known as French Broom, Cape Broom and Montpellier Broom, is a woody perennial shrub and a legume...

 (6 acres), and field mustard

Brassica rapa

Brassica rapa L. , commonly known as turnip, turnip rape, field mustard or turnip mustard is a plant widely cultivated as a leaf vegetable , a root vegetable , and an oilseed .In the 18th century the turnip and...

, but no specific proposal for re-introduction of the lupine was included in the Management Plan.

The Canyon and Urban Planning

The importance of Glen Canyon Park to its surrounding neighborhoods is indicated by a recent community plan for Glen Park

Glen Park, San Francisco, California

Glen Park is a small neighborhood in San Francisco, California, named for the adjacent Glen Canyon Park.-Location:It is at the southern edge of the hills in the interior of the city, to the south of Diamond Heights and Noe Valley, west of Bernal Heights, and east of Glen Canyon Park...

 that contains the following statement: "The Glen Park community’s special character is created by the unique combination of eclectic building styles, pedestrian scale, the layering of green space and buildings climbing into the canyon, public spaces, walkable streets, a compact village, and proximity to transit and the canyon. Every new development project, whether public or private, must incorporate these features based on principles of good design and human scale."

A section of Bosworth Street connects the southern entrance to Glen Canyon Park with the central commercial district of Glen Park that lies about a third of a mile east. This section presents an important opportunity for urban design

Urban planning

Urban planning incorporates areas such as economics, design, ecology, sociology, geography, law, political science, and statistics to guide and ensure the orderly development of settlements and communities....

 because the properties along the north side have remained undeveloped since their acquisition by the City in the 1950s. The community plan proposes that this land be developed into a greenway and pedestrian plaza. The plan also suggests that Islais Creek

Islais Creek

Islais Creek or Islais Creek Channel is a small creek in San Francisco, California...

, which runs underneath this section of Bosworth Street, be "daylighted"

Daylighting (streams)

In urban design and urban planning, daylighting is the redirection of a stream into an above-ground channel. Typically, the goal is to restore a stream of water to a more natural state...

in this section. The plan was formally endorsed by the San Francisco Planning Commission in 2004, but implementation has not been funded as of 2007.

External links

• Friends of Glen Canyon Park, a volunteer citizen stewardship group that was organized in 1986.
• Bay Area Hiker: Glen Canyon Park. A detailed guide for the urban hiker.
• Guide to San Francisco Bay Area Creeks - Islais Creek
• Planned route of the Crosstown Freeway