CDOT – Highway 101/Highway 36, Alton Interchange

Status Completed County Humboldt
Project Type Compensatory mitigation Location 40.54786° N, -124.14553° W Map
Project Area (Acres) 12.93 Last Updated 20 May 2021
Project Abstract The project involves conversion of Highway 101 from a four lane expressway to a four lane freeway between the Van Duzen River Bridge (P.M. 57.0) and Drake Hill Road (P.M. 59.1), approximately two miles south of the City of Fortuna.
Project Groups Caltrans 401 Projects

Project Identification

0100000078 Caltrans - Enterprise Financial Infra-Structure Number
01-29030 Caltrans - Expenditure Authorization
2005032007 SCH - State Clearinghouse Number
1B07140WNHU SWRCB - 401 Certification Letter (e.g., Site Number or WDID)
721085 SWRCB - CIWQS Place Number

Habitat Plan

Site NamePhaseActivitySubActivitiesHabitatSubHabitatAcresActivity StatusWater Regime
HIGHWAY 101/HIGHWAY 36, ALTON INTERCHANGE None Creation/Establishment Unspecified Riverine Wetland Riparian area 1.23 Completed Riparian
HIGHWAY 101/HIGHWAY 36, ALTON INTERCHANGE None Creation/Establishment Unspecified Seasonal Wetland Diked wetland 4.30 Completed Seasonal non-tidal
HIGHWAY 101/HIGHWAY 36, ALTON INTERCHANGE None Enhancement Unspecified Seasonal Wetland Unknown/Unspecified 1.50 Completed
HIGHWAY 101/HIGHWAY 36, ALTON INTERCHANGE None Creation/Establishment Unspecified Unknown/unspecified wetland habitat None 5.90 Completed

Related Habitat Impacts

HabitatAcres LostType of Loss
Unknown/unspecified habitat 0.48 Lost Permanent
Unknown/unspecified wetland habitat 4.49 Lost Permanent
Unknown/unspecified wetland habitat 0.19 Lost Temporary




DateTypeDescriptionSite Name
2013-01-22 Project end date
2009-04-14 Project start date


Contact Unknown California Department of Transportation District 1


No Data

Related CRAM Assessments

Visit DateVersionSite NameWetland TypeIndex Score
No Data
Name File Type Submitted On Submitted By
Mitigation and Monitoring Plan Plan Or Permit 2020-02-26 SFEI, SFEI
Section 401 Water Quality Certification Plan Or Permit 2019-07-08 SFEI, SFEI

How to Use the Habitat Development Curve

Habitat Development Curves (HDCs) are used to determine the developmental status and trajectory of on-the-ground projects to create, restore, or enhance California wetland and stream habitats. Each HDC is based on assessments of habitat condition for different age areas of one habitat type that in aggregate represent the full spectrum of habitat development. The assessments of condition are provided by expert applications of the California Rapid Assessment Method (CRAM). Visit the CRAM website for more information about CRAM.

For each HDC, reference condition is represented by areas of a habitat that consistently get very high CRAM scores, have not been subject to disruptive management practices, and exist within landscapes that are protected and managed for their natural conditions. The horizontal lines intersecting the top of an HDC represent the mean CRAM score and standard deviation of scores for 25 qualifying reference areas.

The age of a project is estimated as the elapsed time in years between the groundwork end date for the project and the date of the CRAM assessment. To add or update a groundwork end date, use the Project Events form in Project Tracker ( The minimum age in years of a non-project area, including any natural reference area, is estimated from all available local information, including historical maps and imagery, historical written accounts, and place-specific scientific studies of habitat development.

An HDC can be used to address the following questions:

  1. At what time in the future will the area of assessed habitat achieve the reference condition or other milestones in habitat development? The HDC can answer this question if the CRAM score for the assessed area is within the confidence interval of the HDC. The answer is the time in years along the HDC between the current age of the assessed area and the future date corresponding to the intersection of the HDC and the reference condition or other milestone.
  2. Is the area of assessed habitat likely to develop faster, slower, or at the same pace as most other areas of the same habitat type? The habitat area is likely to develop faster, slower, or at the same pace if the CRAM score for the area is above, below, or within the confidence interval of the HDC, respectively.
  3. What can be done to improve the condition of the habitat area or to increase its rate of development? HDCs by themselves cannot answer this question. Possible answers can be inferred by the following analysis that involves HDCs:
    1. Examine the HDC for each of the four CRAM Attributes;
    2. Identify the Attribute(s) scoring below the HDC;
    3. For any low-scoring Attribute, examine the component Metric Scores (note: the Metric Scores for any public CRAM assessment in the CRAM database can be obtained through EcoAtlas);
    4. Assume the low score of an Attribute is due to its low-scoring Metric(s);
    5. Consider modifying the design or management of the habitat area in ways that will sustainably increase its score(s) for the low-scoring Metric(s).

For more information about CRAM Attributes and Metrics, including their scientific rationale, see the CRAM Manual.

Display Habitat Development Curves For Wetland Type:

CRAM Site Scores