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Background layers are available in several Calflora applications that use Google Maps, including Observation Hotline.

Background layers are divided into three groups: Region, Climate, and Soil. Click on a group name -- for instance Region -- to see all of the layers within that group. Then click on the name of a layer -- for instance Protected Areas (CPAD) -- and the colored polygons of that layer will be superimposed on top of the Google Map. Note that not all layers are available at all zoom levels.

The map applications can show one background layer at a time. However, County Lines and Streams can be turned on at the same time as a background layer.

The four checkboxes at the bottom control the appearance of colored polygons in the selected background layer. If the appearance of the polygons is too subtle, you can emphasize the outline of each polygon, or ask for darker background colors for each polygon.

Here is an example of the Climate / Precipitation layer with darker background colors and a thick white outline (click to see it "live"):

Please see also this introduction to Calflora Map Applications, which explains how the map cursor works.


From the USGS National Hydrology Dataset

California Protected Areas Database

Version 2018a (December, 2018) from Greeninfo Network

The California Protected Areas Database (CPAD) is a GIS inventory of all protected park and open space lands in California. The database contains lands held in fee ownership by public agencies and non-profits.

The units level of this database is shown in Calflora map applications. Click in an area to see its name.

For areas with restricted access or no access to the public, the warning is included after the name. For instance

San Francisco Watershed Lands - restricted access
  No Access
  Restricted Access
  Park or Open Space area; Public Access
  Federal Land (other than National Parks); Public Access

From CalWater 2.2.

Calflora map applications can show the four levels of this dataset listed on the right. Which level is shown depends on how far in the map is zoomed in.

Level Example
Planning Watershed 3309.811105 Little Burnett Creek
Super Planning Watershed 3309.8111 McLaughlin Canyon
Hydrologic Area 3309.8 Paso Robles
Hydrologic Unit 3309. Salinas

Zip Codes
From United States Census Bureau TIGER/Line Shapefiles

Major Land Resource Areas (NRCS)

  04B Coastal Redwood Belt
  05 Siskiyou - Trinity Area
  14 Central California Coastal Valleys
  15 Central California Coastal Range
  16 California Delta
  17 Sacramento and San Joaquin Valleys
  18 Sierra Nevada Foothills
  19 Southern California Coastal Plain
  20 Southern California Mountains
  21 Klamath and Shasta Valleys and Basins
  22A Sierra Nevada Mountains
  22B Southern Cascade Mountains
  23 Malheur High Plateau
  26 Carson Basin and Mountains
  29 Southern Nevada Basin and Range
  30 Mojave Desert
  31 Lower Colorado Desert

4ETa Zones
4ETa Zones indicating evaopotranspiration (NRCS California)

  b18 - 21inches
  c15 - 18inches
  d12 - 15inches
  e9 - 12inches
  f6 - 9inches
  g3 - 6inches
  h0 - 3inches

EPA Ecoregions
Calflora maps display both Level III Ecoregions and Level IV Ecoregions.

Level III Ecoregions

1. Coast Range
78. Klamath Mountains/California High North Coast
4. Cascades
9. Eastern Cascades Slopes and Foothills
80. Northern Basin and Range
6. Central California Foothilss and Coastal Mountains
7. Central California Valley
5. Sierra Nevada
13. Central Basin and Range
8. Southern California Mountains
14. Mojave Basin and Range
85. Southern California Coast
81. Sonoran Basin and Range

Jepson Flora Project Geographic Subdivisions
Please see Jepson eFlora: Geographic subdivisions.
Polygons are © 1993 - 2019 Regents of the University of California.

Jepson Regions

Northwestern California
Cascade Ranges
Modoc Plateau
Central Western California
Great Valley
Sierra Nevada
East of Sierra Nevada
Southwestern California
Mojave Desert
Sonoran Desert
Each climate and soil layer described here is presented as a abstract factor contributing to the characterization of a location. The choice of which factors to show as layers on Calflora maps is informed by USDA PLANTS Conservation Plant Characteristics (particularly Growth Characteristics), but within the pragmatic bounds of what data is available. The goal is to be able to use these factors as predictors of where various plants are likely to grow.

as prepared by the Prism Climate Group at Oregon State University, and available from the USDA Geospatial Data Gateway.

PRISM data is typically available as a raster, where a cell is 30 arc seconds (~ 800 m) on a side.

CITATION: U.S. Department of Agriculture, Natural Resources Conservation Service, National Geospatial Management Center

Average Annual Precipitation
Annual average precipitation during the period 1971 - 2000.

For predicting where a plant may grow, it is important to know the minimum annual precipitation it requires (and for certain plants, the maximum annual precipitation it will tolerate).

Units: inches per year

157 inches
133 inches
107 inches
81 inches
61 inches
37 inches
17 inches
3 inches

As presented in Calflora map applications, the colors indicating climate layers are continuous. Colors associated with selected values of Annual Precipitation are shown here.

Wet Season
The number of wet months, as derived from monthly average precipitation (1981 - 2010) cell data. For a particular month, an 800 m cell is considered wet if it receives at least 1.3 inches of precipitation.

As a characterization of location, this is similar to annual precipitation, but indicates the duration of a season during which rain is likely.
Units: number of months


July High Temperature
based on average minimum monthly data during the period 1981-2010.

Units: degrees Fahrenheit


December Low Temperature
based on average minimum monthly data during the period 1981-2010.

Units: degrees Fahrenheit


Accumulated Temperature
based on average mean temperature and average minimum temperature monthly data during the period 1981-2010. This is a measure of accumulated heat during those months during which the minimum temperature is greater than 43 ° F (6 ° C). It is related to the concept of degree-days, but unlike degree-days calculated for a particular year, this number is based on average mean temperature. It is roughly equivalent to an annual sum of degree-days during the growing season.

In the context of these climate factors, accumulated temperature can help determine which places are too hot for a plant. It is particularly useful for differentiating very hot places (Death Valley) from moderately hot places (Fresno).
Units: degrees Fahrenheit

See also
A comparative study of different temperature accumulation methods for predicting the start of the Quercus pollen season in Cordoba (South West Spain), H. Garcia-Mozo, C. Galan, M. T. Gomez-Casero and E. Dominguez-Vilches, in Grama 39: 194-199, 2000

Temperature Range
Calculated as July High Temperature minus December Low Temperature per cell. In climate modelling, temperature range is akin to temperature seasonality.

In the context of these climate factors, temperature range is useful for differentiating coastal areas from inland areas. Coastal areas typically have a narrower temperature range than inland areas.
Units: degrees Fahrenheit

Growing Season
The number of consecutive warm months, as derived from average minimum monthy temperature (1981 - 2010) cell data. For a particular month, an 800 m cell is considered warm if the average minimum temperature is at least 43 ° F (6 ° C).

Units: number of months

≤ 1

USDA Hardiness Zone
The map is based on average annual minimum winter temperature, divided into zones by 5 ° F increments. See the USDA Plant Hardiness Zone Map.

Hardiness Zone differs from December Low Temperature above, in that it reflects the lowest temperature that might ever be experienced at a location.

Units: degrees Fahrenheit

5a: -20 to -15
5b: -15 to -10
6a: -10 to -5
6b: -5 to 0
7a: 0 to 5
7b: 5 to 10
8a: 10 to 15
8b: 15 to 20
9a: 20 to 25
9b: 25 to 30
10a: 30 to 35
10b: 35 to 40
11a: 40 to 45

DISCLAIMER: Shapefiles of the hardiness zones for California were purchased and downloaded from Climate Source in February, 2014. They were subsequently modified (chopped into smaller pieces) for display as a map background layer.
USDA Agricultural Research Service Terms of Use: Data: Users may obtain enhanced (high resolution) official USDA Plant Hardiness GIS data in shapefile and raster grid formats from Climate Source, Inc. (www.climatesource.com/PHZM/gis_data.html), subject to Climate Source terms of use. The USDA-ARS and OSU logos must be prominently displayed on any maps derived from the GIS datasets. The data may not be altered in any way without an explicit and prominently displayed disclaimer that the map is not the official USDA Plant Hardiness Zone Map, and USDA-ARS and OSU logos must not be displayed in the modified version.
(See also GIS Data Downloads.)

Climate Source Inc. Notice: This product contains data from The Climate Source and is used herein by permission. Copyright (c) 2014 The Climate Source, www.climatesource.com. All Rights Reserved.
(See also License Agreement.)


See also NRCS Part 618 Soil Properties and Qualities, and
SSURGO Tables and Columns.

Most factors below are based on consideration of all major components of a soil map unit, as per the CTSG algorithm.

CITATION: Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Soil Survey Geographic (SSURGO) Database for California. Available online at //soildatamart.nrcs.usda.gov. Accessed 05/01/2013.

Soil Depth
Minimum depth to the first restrictive layer of the major components of a soil map unit.

For trees and shrubs particularly, it is important to know the minimum soil depth required by the plant.

Units: cm

Soil pH
pH of the major components of a soil map unit, to a depth of 30 cm.

From Soil Properties and Qualities:

    "Soil reaction" is a numerical expression of the relative acidity or alkalinity of a soil. ... Soils that have a pH of approximately 6 or 7 generally have the most ready availability of plant nutrients.

See also this Calflora analysis of
how many plants tolerate each soil pH.
6.5 is the pH tolerated by the most plants.

  Class pH
  Ultra acid 1.8 to 3.4
  Extremely acid 3.5 to 4.4
  Very strongly acid 4.5 to 5.0
  Strongly acid 5.1 to 5.5
  Moderately acid 5.6 to 6.0
  Slightly acid 6.1 to 6.5
  Neutral 6.6 to 7.3
  Slightly alkaline 7.4 to 7.8
  Moderately alkaline 7.9 to 8.4
  Strongly alkaline 8.5 to 9.0
  Very strongly alkaline 9.1 to 11.0

Soil CaCO3
The maximum calcium carbonate equivalent in the major components of a soil map unit, to a depth of 30 cm.

From Soil Properties and Qualities:

    “Calcium carbonate equivalent” is the quantity of carbonate (CO3) in the soil expressed as CaCO3 and as a weight percentage of the less than 2 mm size fraction.
    ... The availability of plant nutrients is influenced by the amount of carbonates in the soil. This is a result of the effect that carbonates have on soil pH and of the direct effect that carbonates have on nutrient availability.
Units: percent

Soil Salinity
as indicated by electrical conductivity. The maximum conductivity of the major components of a soil map unit, to a depth of 30 cm.

From Soil Properties and Qualities:

    Electrical conductivity is a measure of the concentration of water-soluble salts in soils. It is used to indicate saline soils. High concentrations of neutral salts, such as sodium chloride and sodium sulfate, may interfere with the absorption of water by plants ... [and] may also interfere with the exchange capacity of nutrient ions...

Units: mmhos / cm
  Class Conductivity in mmhos / cm
  Non-saline0 to <2
  Very slightly saline2 to <4
  Slightly saline4 to <8
  Moderately saline8 to <16
  Strongly saline≥16

Soil Texture
Texture as used here is based on the particle size of the major components of a soil map unit, and other indicators. A typical categorization of textures is shown on the right (image from the NRCS Soil Texture Calculator).

From Soil Properties and Qualities:

    "Particle size” is the effective diameter of a particle as measured by sedimentation, sieving, or micrometric methods. ...
    The broad classes are
    • clay  [<0.002 mm]
    • silt    [0.002 to 0.05 mm]
    • sand [0.05 to 2.0 mm]...



California Climate Data Archive


Plant Tolerances:

Las Pilitas Nursery (native plant ranges and tolerances)