The Santa Clara Subbasin comprises the complex layers of sandy gravel and clay that form the floor of the Santa Clara Valley. Layers of sandy gravel are easily permeable to water, and form aquifers that can store vast amounts of groundwater. The subbasin aquifers transmit, filter, and store water, and reach a depth of more than 1000ft (300m) in some places. Layers of relatively impermeable clay separate aquifer layers from each other.
In the middle of the subbasin, a continuous clay layer prevents surface water from seeping into the aquifer layers below. Groundwater recharge cannot occur in this confined zone, which is several miles across. Around the edge of the basin, there is no continuous clay layer. In this unconfined recharge zone, surface water can seep (percolate) through the earth's layers into the aquifer, recharging the groundwater.
During the first half of the 20th century, increasing population led to increasing groundwater extraction. The resulting reduction in artesian pressure levels caused the land above the aquifer to subside as much as 13ft (4m). The Santa Clara Valley Water District (originally the Santa Clara Valley Water Conservation District) was created both to ensure a reliable water supply and to prevent land subsidence.
The district works to reduce the demand on groundwater aquifers, but the amount of groundwater pumped from wells still exceeds the natural recharge rate. Various groundwater recharge facilities make up the difference. Examples include the nearby recharge ponds, as well as structures along managed creeks that convert the water flow into a series of pools. Recent studies have shown that current management practices have halted land subsidence.
Logging This EarthCache:
To log this EarthCache, you must send me your answers to the following questions, and upload a photo of you (or a personal item) on the bridge at the posted coordinates. Logs dated prior to 2019-07-01 are exempt from the photo requirement. Additional non-spoiler photos are always appreciated.
When you send me email, please include the EarthCache name and GC code: Santa Clara Subbasin (GC5NB5G)
Questions to Answer
- From the bridge at the posted coordinates, you can see various features related to groundwater recharge. Each of the four signs listed as waypoints provides the name of one of those features. What are the four named features?
- Are these four named features within the confined zone of the Santa Clara Subbasin? How do you know?
- Where does the water in the nearby recharge ponds originally come from?
Logistics
The Los Gatos Creek Trail and the nearby Los Gatos Creek County Park are open 8 AM to sunset, year round. Please respect the trail and park hours. There is a parking fee at the park, although I have used free on-street parking near the posted trailhead waypoint.
To answer the questions correctly, you will need information in the geocache description above, as well as information on the 4 signs listed as waypoints. Three of those signs are "Discover Water" benches like the one shown in the banner photo above. The remaining sign is a bronze plaque mounted at chest height; if you have difficulty spotting it, see the attached spoiler photo.
The terrain rating reflects signs that are off the paved trail, plus a round-trip hike (from the posted trailhead) of a little more than 0.6mi (1km).
See Also
Additional internet research is not needed to answer the questions for this EarthCache; you need only the text and images above, and the signs at the site. But the following resources may be of interest to those who wish to learn more about the Santa Clara Subbasin:
