Dirt.

Turns out the USDA has this semi-handy-dandy on-line soil map thingy!

And it seems the local dirt what we got here under SVR Central has a name:

Santa Clara Area, California, Western Part

145—Urbanland-Hangerone complex, 0 to 2 percent slopes, drained

Map Unit Setting

• Elevation: 0 to 220 feet
• Mean annual precipitation: 14 to 24 inches
• Mean annual air temperature: 57 to 61 degrees F
• Frost-free period: 275 to 325 days

Map Unit Composition

• Urban land: 70 percent
• Hangerone, drained, and similar soils: 25 percent
• Minor components: 5 percent

Description of Urban Land

Setting

• Landform: Basin floors
• Landform position (three-dimensional): Talf
• Down-slope shape: Linear
• Across-slope shape: Linear
• Parent material: Disturbed and human transported material

Description of Hangerone, Drained

Setting

• Landform: Basin floors
• Landform position (three-dimensional): Talf
• Down-slope shape: Linear
• Across-slope shape: Linear
• Parent material: Alluvium derived from metamorphic and sedimentary rock and/or alluvium derived from metavolcanics

Properties and qualities

• Slope: 0 to 2 percent
• Depth to restrictive feature: More than 80 inches
• Drainage class: Poorly drained
• Capacity of the most limiting layer to transmit water (Ksat):Moderately low to moderately high (0.06 to 0.20 in/hr)
• Depth to water table: More than 80 inches
• Frequency of flooding: None
• Frequency of ponding: None
• Calcium carbonate, maximum content: 25 percent
• Gypsum, maximum content: 2 percent
• Maximum salinity: Nonsaline to very slightly saline (0.2 to 4.0 mmhos/cm)
• Sodium adsorption ratio, maximum: 5.0
• Available water capacity: Moderate (about 8.3 inches)

Interpretive groups

• Farmland classification: Not prime farmland
• Land capability classification (irrigated): 2s
• Land capability (nonirrigated): 3s
• Hydrologic Soil Group: C

Typical profile

• 0 to 9 inches: Clay
• 9 to 17 inches: Clay
• 17 to 27 inches: Clay
• 27 to 35 inches: Clay
• 35 to 45 inches: Clay loam
• 45 to 72 inches: Gravelly loam
• 72 to 89 inches: Clay

Minor Components

Bayshore

• Percent of map unit: 2 percent
• Landform: Basin floors
• Landform position (three-dimensional): Talf
• Down-slope shape: Linear
• Across-slope shape: Linear

Clear lake

• Percent of map unit: 2 percent
• Landform: Basin floors
• Landform position (three-dimensional): Talf
• Down-slope shape: Linear
• Across-slope shape: Linear

Embarcadero

• Percent of map unit: 1 percent
• Landform: Basin floors
• Landform position (three-dimensional): Talf
• Down-slope shape: Linear
• Across-slope shape: Linear

Now, knowing that, I keep wanting to give "Hangerone" an Italian pronunciation... and I guess "Urbanland" must be the name of some English dude, right?

Anyway: heavy clay landfill.  Needs big additions of gypsum and compost to be usable for anything but putting stuff on.

The neighborhood in Palo Alto where I grew up is on the same stuff.

And this explains my mystification when I look at aerial views of Appalachia, see bald spots, and wonder, "What's that pale tan stuff?"  (Answer: silty loam.)