Chapter 17.90


17.90.010    Established.

17.90.020    General requirements.

17.90.030    Gradient.

17.90.040    Minimum widths of right-of-way, graded portion and paved surface.

17.90.050    Minimum widths of right-of-way, graded portion, base and paved surface.

17.90.060    Construction standards.

17.90.070    Curbs and gutters required when.

17.90.080    Materials.

17.90.090    Road mix surfacing specifications.

17.90.100    Asphalt concrete specifications.

17.90.120    Drainage standards.

17.90.130    Clear and grub standards.

17.90.140    Erosion control standards.

17.90.150    Acceptance of dedication and maintenance.

17.90.160    Final subdivision public report.

17.90.180    Caltrans Standard Specifications to govern.

17.90.010 Established.

Minimum improvement specifications for the design and improvement of roads and streets are established as set forth in this chapter.  Note: additional structural thickness of the roadbed may be required when the traffic index is high and/or when the R value of the subgrade is low.  (Ord. 664 §1(part), 1978).

17.90.020 General requirements.

A.    In no case shall a culvert across a roadway be less than eighteen inches in diameter.

B.    If adverse conditions exist, the rough grading of driveways shall be performed prior to placing the surfacing on the streets.  (Ord. 664 §1(part), 1978).

17.90.030 Gradient.

A.    The minimum gradient for all streets shall be one-half percent.

B.    The maximum gradient for all streets below two thousand feet elevation shall be fifteen percent.

C.    The maximum gradient for all streets above two thousand feet elevation shall be ten percent.  (Ord. 664 §1(part), 1978).

17.90.040 Minimum widths of right-of-way, graded portion and paved surface.

The minimum widths of right-of-way, graded portion, road base and road surfacing are shown in Table 12.08.030 for publicly maintained roads and Table 12.08.035 for privately maintained roads and driveways.  The tabulation of minimum road requirements as set forth in Section 12.08.030 is amended.  (Ord. 1734 §7(part), 2014:  Ord. 664 §1(part), 1978).

17.90.050 Minimum widths of right-of-way, graded portion, base and paved surface.

As specified in minimum construction requirements table in Section 12.08.030 and private roads construction table in Section 12.08.035.  (Ord. 1734 §7(part), 2014:  Ord. 664 §1(part), 1978).

17.90.060 Construction standards.

A.    The base material will be no less than the thickness shown on Exhibit A, attached to the ordinance codified in this chapter, of crushed rock or screened gravel, except where, in the opinion of the county engineer, a lesser thickness is justified.

B.    A liquid asphalt penetration treatment where required in Exhibit A, attached to the ordinance codified in this chapter, of SC-250 grade asphalt shall be applied at the rate of at least 0.3 gallon per square yard to the entire width of gravel base.

C.    A paved surface where required in Exhibit A, attached to the ordinance codified in this chapter, of road-mixed asphalt or asphalt concrete pavement shall be applied to a compacted thickness of at least two inches.  The design of the mix shall have the written approval of the county engineer.  (Ord. 664 §1(part), 1978).

17.90.070 Curbs and gutters required when.

Curbs and gutters for residential subdivision for less than forty thousand square-foot lots shall be placed on streets where it is necessary to provide on-street parking and/or control of drainage.  (Ord. 664 §1(part), 1978).

17.90.080 Materials.

A.    The mineral aggregate shall be free from vegetable matter and other deleterious substances and shall be of such character that it can be compacted readily under watering and rolling to form a firm and stable base.

B.    Broken or crushed gravel.

C.    Natural material having essentially the same qualities of angularity or surface irregularities and roughness as broken, stone and conforming to the specified quality and requirements when combined within the required grading limits.

D.    1.  The combined mineral aggregate shall be of such size that the percentage composition by weight, as determined by laboratory sieves, will conform to one of the following gradings:


1 1/2-inch


Sieve Size






1 1/2"






3/4" 50--90



No. 4



No. 200

3--12 Dry

3--12 Dry

No. 200

3--15 Wet Wash

3--15 Wet Wash

All rattler tests waived


Resistance Value (R Value)

72 Minimum

Sand Equivalent

25 Minimum

2.    When mineral aggregate does not contain sufficient natural cementing material to be compacted readily under water and rolling, there shall be added to and incorporated in it, a binder material consisting of rock screenings, or disintegrated granite, or other cementitious material approved by the county engineer.  Binder material, if required, shall be incorporated with the aggregate by a method approved by the county engineer, that will uniformly distribute the material throughout the aggregate.  When binder material is added to the mineral aggregate, the combination shall conform to all the quality and grading requirements specified for the aggregate.

Note:  If a natural material is found, by experience or otherwise, to be of a quality equal to the above specifications, the county engineer may authorize the use of such material.

E.    1.    The aggregate for subbase material shall be clean and free from vegetable matter and other deleterious substances and shall be of such quality that it will bind readily to form a firm, stable subbase.

2.    The percentage composition by weight of aggregate subbase shall conform to the following gradings:

Sieve Size

Percentage Passing



2 1/2"


No. 4


No. 200


Resistance (R Value)

55 Minimum

Sand Equivalent

20 Minimum

3.    Aggregate subbase material may be obtained by breaking up, crushing, screening, wasting, wasting material or any combination thereof, or use any other process that will produce the required grading.  Aggregate for subbase shall be delivered to the roadbed as uniform mixtures and shall be spread in layers or windrows without segregation.  (Ord. 1734 §7(part), 2014; Ord. 664 §1(part), 1978).

17.90.090 Road mix surfacing specifications.

A.    Road-mixed surfacing shall consist of mineral aggregate and bituminous binder mixed on the road by the road mix methods, or mixed off the roadbed by either road mix or plant mix methods.  The mixture shall be spread and compacted on a prepared base in conformity with the lines, grades and dimensions shown on the plans or typical cross sections or specified in this section.

B.    Bituminous Materials.  Bituminous binder to be mixed with the mineral aggregate shall be liquid asphalt of a grade designated by the county engineer.

C.    Mineral Aggregate.

1.    The mineral aggregate for road-mixed surfacing shall conform to the requirements for mineral aggregate for Type C plant-mixed surfacing, or it may consist of the material in place on the roadbed, or a combination of two or more of these materials, all as required by these specifications, such material to meet the grading and qualities specified.

2.    Mineral aggregate for Type C plant-mixed surfacing to be used for road-mix surfacing, shall conform to the following gradings and qualities:


Sieve Size

3/4 inch


1/2 inch














No. 4



No. 30



No. 200



Stabilometer Value

32 Min.


0.030 Max.

Sand Equivalent

30 Min.

D.    Mixing.  The mineral aggregate and liquid asphalt shall be combined in a ratio as specified, such mixing shall continue until the mixture is thoroughly combined.  There shall be no small portions or goublets of unmixed oil visible in the mixture, nor shall there be any uncoated particles of mineral aggregate visible.  (Ord. 664 §1(part), 1978).

17.90.100 Asphalt concrete specifications.

Asphalt concrete shall be Type B, one-half-inch maximum and shall conform to the provisions in Section 39 "Asphalt Concrete" and Section 92 "Asphalts" of the current state of California Caltrans Standard Specifications.  (Ord. 664 §1(part), 1978).

17.90.120 Drainage standards.

A.    Roadside ditches shall be designed to carry runoff from the road section only.  Roadside ditches shall not be used as major drainage channels.  Drainage ditches in easements shall be provided to discharge water from the roadside ditches.  The roadside ditches shall have minimum depth of one foot unless otherwise authorized.

B.    Natural drainage channels shall be retained and not realigned if at all possible.  These channels shall be in drainage easements, and shall not encroach on road right-of-way.

C.    A drainage channel (constructed or natural) contained in an adequate drainage easement must be provided for all roadside water leaving the right-of-way.

D.    Drainage areas of greater than one hundred acres shall be designed to pass a one hundred-year storm utilizing available head.  Areas of less than one hundred acres shall be designed to pass a twenty-five year storm with no more than a three-foot head on the culvert.  The design flow may be determined by a recognized method preferred by the engineer.  Flow determination calculations shall be submitted with the plans and specifications for review.

E.    Minimum culvert size is eighteen inches, 16 gauge corrugated steel pipe, (heavier gauge to be determined by height of fill.)

F.    In general, culverts shall be used which meet the minimum requirements of the state of California Division of Highways.  Where concrete pipe is used, it shall be C-76 with Class III used in road right-of-ways.

G.    Neither aluminum nor helically corrugated pipe shall be allowed.

H.    Culverts or drainage structures should be placed at intervals of not more than five hundred feet.

I.    Minimum cover over drainage structures to be eighteen inches.

J.    All culverts shall have a minimum cover of eighteen inches and be protected at both ends by riprap, rock masonry walls or concrete head wall, or shall be extended, three feet beyond the fill on the lower side except where drop inlets or flared-end sections have been specified by the engineer, and approved by the county engineer.  (Ord. 664 §1(part), 1978).

17.90.130 Clear and grub standards.

Clearing and grubbing shall be done in accordance to Section 16 of the Caltrans Standard Specifications.  (Ord. 664 §1(part), 1978).

17.90.140 Erosion control standards.

Cut banks, fill slopes, median, etc., shall have erosion control in accordance with Section 20 of the Caltrans Standard Specifications if necessary as determined by the county engineer.  (Ord. 664 §1(part), 1978).

17.90.150 Acceptance of dedication and maintenance.

The county shall accept the dedication and maintenance of those roads constructed pursuant to any parcel map or subdivision map that meets the full paved design criteria therefor; provided, that such roads are contiguous to a publicly maintained road system and that the requirements of Sections 12.08.082 and 12.08.084 are met.  (Ord. 1194 §2, 1989).

17.90.160 Final subdivision public report.

The subdivider shall prepare a final subdivision public report similar to that required by the state of California Department of Real Estate, which shall be recorded concurrently with the filing of the final parcel map.  Such report shall describe the availability of, and the conditions thereof, of the following services: water, sewage, fire protection, electric, natural gas, telephone, garbage disposal, streets and roads, recreation, and whatever special assessment district.  (Ord. 664 §1(part), 1978).

17.90.180 Caltrans Standard Specifications to govern.

The current Caltrans Standard Specifications shall be the standards by which all improvements, contracts and/or agreements shall be governed.  (Ord. 664 §1(part), 1978).