Los Peñasquitos Lagoon
[3] Due to the fast rise of the sea level at the end of the last glacial period (6000 years BP) the lagoon became a deep bay with the rocky shores.
As the sea level rise slowed down, the sediment carried by the streams started to accumulate, and the sandy beaches appeared around 4000 years BP.
A "high wall composed of small rocks" was located along the beach side of the lagoon (the route of the modern North Torrey Pines Road).
[9] In the 19th century the valley was used for crops, with Rancho Los Peñasquitos being the first land grant (1823) within the limits of the modern San Diego County.
First railroad line, a California Southern Railroad link between National City and Oceanside passed through the eastern part of the area in 1881–1882,[15] with a "Beach Shingle" spur line (also known as “Sea Wall Spur”[11]) running on the north side to the beach in order to transport the construction materials used to pave the streets in San Diego.
[15] As a result, three transportation links intersect the lagoon: Highway 101 runs along the beach on the western side, Santa Fe Railroad line crosses in the center, Interstate 5 lies in the east.
[11] However, in 1925, the Santa Fe Railroad built a single-track roadbed causeway embankment down the center of the lagoon for its Surf Line, which still is in use today on a daily basis by the Coaster and Pacific Surfliner as well as BNSF Railway freight trains.
This embankment severely restricted the normal historical lagoon drainage for the first time, and changed the tidal flow and current pattern.
Even though the bridges were replaced, this area was not double-tracked because it is possible that these tracks will eventually be bypassed by a two-track tunnel underneath Del Mar.
[18] When the Pacific Coast Highway (U.S. Route 101 in California) was expanded in the 1930s, the roadbed along the beach was heightened, and a bridge was built over the mouth the lagoon.
[20] According to LPL Foundation and the State Coastal Conservancy, this fully paved parking lot significantly altered the lagoon's hydrology.
These effects include drops in photosynthetic productivity, higher concentrations of heavy metals, and overall loss of ecosystem biodiversity within the estuary.
[23][24] In addition to ecological impacts, sedimentation in the Los Peñasquitos watershed has led to significant issues within its storm water infrastructure.
Specifically, sediment accumulation in flood control channels has greatly reduced original storm water conveyance capacity.
[26][27] Despite the need for sufficient flood control through regular channel maintenance, the extensive permitting process involved requires selection and planning that extends nearly two years before any service activities.
[30] In 1985, the California Coastal Conservancy created the Los Peñasquitos Lagoon Enhancement Plan to deal with a number of human-caused problems.
[17] The management program is developed by Los Peñasquitos Lagoon Foundation and California State Parks[16] is being implemented since 1985[17] with input from Pacific Estuarine Research Laboratory and the Tijuana River NERR.
[38] This helped considerably in keeping the lagoon much cleaner once the new station came on-line, however there are still spills, with the most recent being on September 9, 2011, when an estimated 1.9 million US gallons (7,200 m3) of raw sewage was released due to a county-wide power outage.
[40] Pump Station 65 was rebuilt and relocated in 1996 to sit on the edge of the lagoon next to a now-closed portion of Sorrento Valley Road.
Closing the road has improved access to a wildlife corridor for deer, fox, coyote, bobcat and spotted skunk to enter and exit the Preserve.
[45] In 2009 one boy developed flu-like symptoms and became delirious a few days after having had a picnic near Los Peñasquitos Lagoon, and needed to be hospitalized for WNV infection, presumably acquired by mosquito bite.
Although mountain lions (Felis concolor) are now rare in the Torrey Pines and Los Peñasquitos Lagoon area, likely as a result of habitat fragmentation,[47] mountain lion tracks and scat were reported between Interstate 5's bridge and Los Peñasquitos Lagoon in 2000 by the Conservation Biology Institute in Encinitas.
It skirts the southern edge of the wetland for 1.5 miles from North Torrey Pines Road and becomes Flintkote Avenue in Sorrento Valley, San Diego.
