3. Affected Environment This chapter presents relevant information about the physical, biological, cultural, and socioeconomic environment within and surrounding the San Diego NWR. 3.1 Environmental Setting 3.1.1 Location and Property Description The San Diego NWR, including the Otay-Sweetwater Unit and Del Mar Mesa Vernal Pool Unit, is located in southwestern San Diego County (refer to Figure 1-1). The largest unit within the Refuge boundary is the Otay-Sweetwater Unit, which as of August 2013 consisted of 11,470 acres of several noncontiguous blocks of undeveloped land (refer to Figure 1-3). For planning and environmental assessment purposes, we have grouped these blocks of land into five distinct management areas: McGinty Mountain, Las Montañas, Sweetwater River, San Miguel Mountain, and Otay Mesa and Lakes (refer to Figure 1-6). These management areas are characterized by a striking diversity of landforms associated with the southwestern terminus of the Peninsular Range. The Sweetwater River extends through northern and western portions of the Otay- Sweetwater Unit, while the eastern and southern boundaries of this Unit are border by the rolling foothills and incised canyons of Sycuan Peak, Jamul Mountains, and Otay Mountain. The 60-acre Del Mar Mesa Vernal Pool Unit is located approximately 20 miles north of downtown San Diego and four miles east of the Pacific Ocean (refer to Figure 1-5). These parcels include areas of level mesa top and deeply eroded canyons with steep slopes. 3.1.2 Regional Context The lands included within the San Diego NWR are identified as core biological resource areas in the MSCP Plan (City of San Diego 1998a) prepared for a 900-square-mile area in southwestern San Diego County. This regional habitat conservation planning effort is anticipated to result in the creation of a regional habitat preserve network that includes approximately 172,000 acres of conserved lands (City of San Diego 1998a) managed by a variety of agencies and non-governmental organizations. The large expanses of undeveloped land that have been preserved to date include much of the remaining intact coastal lowland southern California habitats that support significant populations of endangered, threatened, and sensitive plants and wildlife. Conservation of the lands, major watercourses, and smaller drainages within the Refuge boundary is an essential component of the regional effort to protect the water quality in San Diego County’s bays and estuaries. The Del Mar Mesa Vernal Pool Unit is located within the Peñasquitos Watershed, with water from this area draining into Los Peñasquitos Lagoon. The lands within the Otay-Sweetwater Unit are included within the Sweetwater River and Otay River watersheds, both of which are included within the greater San Diego Bay watershed. 3.2 Physical Environment Elements of the physical environment include topography, visual quality, geology and soils, agricultural resources, mineral resources, paleontology, hydrology and water quality, climate and climate change, air quality, greenhouse gas emissions, and contaminants. ────────────Draft Comprehensive Conservation Plan and Environmental Assessment 3-1 Chapter 3 ────────────────────────────────────────────── 3.2.1 Topography and Visual Quality The landforms that currently characterize southwestern San Diego County are the result of millions of years of geological processes ranging from erosion and sediment deposition to crustal uplifting and seismic and volcanic activity (Walawender no date). Two of the three distinctive geographic regions of San Diego County are represented within the Refuge: the low-lying coastal plain and the mountainous Peninsular Range (County of San Diego 2011). The flat mesa and steep canyon formations common along the coastal plain characterize the Del Mar Mesa Vernal Pool Unit, while the Otay-Sweetwater Unit is characterized by the broad floodplain created by the Sweetwater River and rolling to steep and often rocky foothills of the Peninsular Range. Elevations on Del Mar Mesa range from about 320 feet above mean sea level (MSL) in the canyon bottoms to about 400 feet above MSL on the mesa. Within the more topographically diverse Otay- Sweetwater Unit, the elevations range from 300 feet above MSL along the Sweetwater River floodway to just over 2,300 feet above MSL near the top of San Miguel Mountain. 3.2.1.1 Site Topography Topography of the McGinty Mountain Area The McGinty Mountain area includes approximately 2,080 acres in the northern portion of the Otay-Sweetwater Unit. The major topographic feature within this area is, of course, McGinty Mountain, but there are other topographic features that help define this portion of the Refuge. The northernmost property included within the Refuge’s McGinty Mountain area is located to the north of Dehesa Road and east of Willow Glen Drive, near a major bend in the Sweetwater River (Figure 3-1). This 74-acre parcel preserves a portion of the lower southwestern slopes of Dehesa Mountain. These generally steep, south-facing slopes, which support southern mixed chaparral vegetation, range from 1,100 feet above MSL at the northern property line to about 480 feet above MSL at the edge of Dehesa Road. Just to the south, along the southern edge of the Sweetwater River floodplain, are the steep lower slopes of McGinty Mountain. McGinty Mountain, the most prominent feature in this area, is fairly steep with a major north-south trending ridge reaching a peak elevation of 2,183 feet above MSL. The McGinty Mountain area is generally bordered on the north and west by the Sweetwater River, on the east by Sloane Canyon and Beaver Hollow, and on the south by Jamacha Valley and residential development within the community of Jamul. Another prominent feature in this area is a nearly level mesa that occupies the northwestern portion of the mountain at about 1,100 feet above MSL. McGinty Mountain is transected by several north-south and northwest-southeast oriented seasonal drainages that ultimately flow into the Sweetwater River. The steepest slopes in this area tend to be located at the lower elevations of the mountain, about 800 to 900 feet above MSL, in an area adjacent to the Sweetwater River drainage. The slopes drop quickly to about 400 feet above MSL at the edge of the floodplain. Following south, down the ridge from the peak of McGinty Mountain, is a small 19-acre parcel (the Peg Leg parcel) that includes the northern end of a narrow ridge with an elevation of about 1,500 feet above MSL. This ridge is flanked by relatively steep slopes to the east and west. To the south of the Peg Leg parcel is another Refuge parcel located adjacent to Jamul Drive. The drainages on this parcel ultimately merge downstream to form Mexican Canyon. 3-2 San Diego National Wildlife Refuge ───────────────────────────── ───────────────────────────────────────── Affected Environment Figure 3-1. Topographic Character of the McGinty Mountain Area ────────────Draft Comprehensive Conservation Plan and Environmental Assessment 3-3 Chapter 3 ────────────────────────────────────────────── Topography of the Las Montañas Area To the south and separated from the McGinty Mountain area by Jamacha Valley and Mexican Canyon is the Las Montañas area. This part of the Refuge is bisected by Highway 94 (Figure 3-2). The northern portion of this 1,035-acre management area is characterized by predominately west-facing, steeply sloping terrain that extends down to Mexican Canyon. Elevations range from just over 1,200 feet above MSL in the east to about 700 feet above MSL in the west. The terrain in the southern portion of Las Montañas consists of a series of rocky hillsides that extend down to a prominent drainage, Steele Canyon Creek, that flows along the south side of Highway 94. Another steep drainage that extends through this area begins at the south end of the property, flowing northwest through the parcel until it joins Steele Canyon Creek. More than half of the Las Montañas area consists of slopes with gradients in excess of 25 percent. The area with the highest percentage of slopes exceeding a 50 percent slope gradient is located to the north of Highway 94 (Dudek & Associates 1996). Rock outcrops are common in the steeper portions of the site, and stands of coast live oak are present along some of the major drainages. Prior to acquisition by the Service, portions of the site to the south of Highway 94 were graded in accordance with county-approved plans for a golf course. Natural recruitment of native vegetation has occurred in many of these areas, but evidence of prior grading activity remains. Topography of the Sweetwater River Area Near the western terminus of Steele Canyon is the Sweetwater River area of the Otay- Sweetwater Unit (Figure 3-3). This portion of the Refuge encompasses about 1,950 acres and is located to the north and south of Highway 94 along the Sweetwater River drainage. The 475 acres located to the north of Highway 94 are characterized by an east to west trending ridge that extends to about the center of the property where it reaches a high point of 836 feet above MSL. The steep north, south, and west-facing slopes of the ridge are also included within the Refuge. To the north and west of these steep slopes, the Refuge includes portions of the Sweetwater River floodplain (an area often referred to as Jamacha Valley). The Sweetwater River area located to the south of Highway 94 is characterized by steep sloping terrain that is bisected by the Sweetwater River. The slopes to the east of the river, the lower slopes of San Miguel Mountain, range from about 800 feet above MSL at the high point down to about 300 feet above MSL at the base of the slope. The terrain to the west of the river is characterized by a narrow ridge surrounded by steep slopes to the northwest and southeast.