Madrona Vernal Marsh and Pools EarthCache

Posted coordinates are for parking and the Nature Center.

The Madrona Marsh Preserve and Nature Center are open Tuesdays through Sundays 10:00 am - 5:00 pm and closed on holidays and during inclement weather. Admission is free.

The primary paths of the Preserve are hard-packed sandy soil, and most are wheelchair-accessible, except right after a heavy rain.

The Madrona Marsh Preserve and Nature Center are open Tuesdays through Sundays 10:00 am - 5:00 pm. The Preserve is closed on holidays and during inclement weather.

	View from the bench near the Measuring Pole, January 8, 2016

The Madrona Marsh is one of the last vernal marshes remaining in the South Bay area of the Los Angeles Basin. An extensive wetland system once connected inland areas ranging from the Ballona Wetlands in Marina Del Rey on the north to the Dominguez Watershed and extending south to San Pedro Bay. Today, the watershed area is 96% developed, with a system of concrete storm drains and flood control channels which direct surface runoff to the Los Angeles Harbor and Santa Monica Bay. Other remaining wetland oases in the area include the Gardena Willows Wetland Preserve and Machado Lake in Harbor City.

What is a Vernal Marsh?
A vernal marsh is a low-lying area that fills seasonally with rainwater from winter and spring (vernal) storms, and then typically dries up by late summer. The vernal marsh is contained within its own shallow geologic drainage basin and does not have a natural downstream outlet. Generally, the pools are shallower and more ephemeral, the marshes are filled with water for a longer period of time.

Formation of the Madrona Vernal Marsh and Pools
The El Segundo Sand Dune system once covered a large area of the South Bay coastline. Onshore winds carried only the smallest sand grains inland, to the eastern edge of the dune system where the sand was deposited. Madrona Marsh is located in a natural depression in this back dune area. During winter storms, runoff from neighborhoods to the north and east collect in the sump at the southeast corner of the Preserve, where it undergoes a biofiltration process before being returned to the wetlands. The water you see in the Marsh is this filtered drainage water, along with water from natural precipitation. The water percolates downward through the fine sand deposits until reaching more impermeable silt and clay layers below, creating ponded water on the surface. The nine Vernal Pools are filled solely by precipitation. As more water collects throughout the rainy season, the surface area of the vernal pool increases as does the water depth.

Observations at the start of the 2016 El Niño Season
At the time of our most recent visit, five acres of the 43-acre Preserve were under water. Conditions should change dramatically over the next few months with this year's predicted El Niño storms.

Logging requirements:
Please remember this is an EarthCache, there is no physical container to find at the posted coordinates.

Waypoint MP brings you to a location map sign of the Madrona Marsh Preserve, just inside the Preserve gates. On the map, note the location of Vernal Pools 1 - 9 and the location of the Measuring Pole, which are also listed under Additional Waypoints. To log this Earthcache as "Found", take a walk on the Preserve trails and send us a message through our profile on geocaching.com with your answers to the following items:

1. The text "GC3B3CH Madrona Marsh Earthcache" on the first line.
2. The number of people in your group.
3. Date of your visit.
4. Which of the nine Vernal Pools were filled with water?
5. Estimated water level on the Measuring Pole at the time of your visit? The black lines on the pole mark elevations in feet above sea level ranging from 73' at the lowest line to 77' at the top line.
6. Your observations of the soil in the Preserve, and why it would contribute to formation of a Vernal Marsh in this area.
7. Not required but helpful to observe the seasonal changes in the Vernal Pools over time: Post a photograph of the water with your online log.
8. After sending us the required answers, go ahead and log your find. Please do not post your answers in your online log.

What Else Can You Do At Madrona Marsh?
Visit the Nature Center to learn more about plant and animal life in the Marsh. Watch birds - the Marsh provides a resting spot for migrating birds along the Pacific Flyway. Hundreds of native and non-native species have been observed here over the years. Check out the Friends of Madrona Marsh calendar for scheduled walks, classes, activities for kids, and volunteer opportunites.

Resources:
Wikipedia.org
Friends of Madrona Marsh Preserve
Los Angeles Regional Water Quality Control Board Dominguez Channel Watershed Management Area
The Ecology of Southern California Vernal Pools, U.S. Fish and Wildlife Service, 1987.