California: California Highway Patrol, Sacramento, CA. 916-445-1865.

1. No vehicle shall be driven or moved on any highway unless the vehicle is so constructed, covered, or loaded as to prevent any of its contents or load other than clear water or feathers from live birds from dropping, sifting, leaking, blowing, spilling, or otherwise escaping from the vehicle.
2.  
1. Aggregate material shall only be carried in the cargo area of a vehicle. The cargo area shall not contain any holes, cracks, or openings through which that material may escape, regardless of the degree to which the vehicle is loaded, except as provided in paragraph (2).
2. Every vehicle used to transport aggregate materials, regardless of the degree to which the vehicle is loaded, shall be equipped with all of the following:
1. Properly functioning seals on any openings used to empty the load, including, but not limited to, bottom dump release gates and tailgates.
2. Splash flaps behind every tire, or set of tires, regardless of position on the truck, truck tractor, or trailer.
3. Center flaps at a location to the rear of each bottom dump release gate as to trucks or trailers equipped with bottom dump release gates. The center flap may be positioned directly behind the bottom dump release gate and in front of the rear axle of the vehicle, or it may be positioned to the rear of the rear axle in line with the splash flaps required behind the tires. The width of the center flap shall extend not more than one inch from one sidewall to the opposite sidewall of the inside tires and shall extend to within five inches of the pavement surface, and shall be not less than 24 inches from the bottom edge to the top edge of that center flap.
4. Fenders starting at the splash flap with the leading edge of the fenders extending forward at least six inches beyond the center of the axle which cover the tops of tires not already covered by the truck, truck tractor, or trailer body.
5. Complete enclosures on all vertical sides of the cargo area, including, but not limited to, tailgates.
6. Shed boards designed to prevent aggregate materials from being deposited on the vehicle body during top loading.
3. Vehicles comprised of full rigid enclosures are exempt only from subparagraphs (C) and (F) of paragraph (2) of subdivision (b).
4. For purposes of this section, "aggregate material" means rock fragments, pebbles, sand, dirt, gravel, cobbles, crushed base, asphalt, and other similar materials.
5.  
1. On and after September 1, 1990, in addition to subdivisions (a) and (b), no vehicle shall transport any aggregate material upon a highway unless the material is covered
2. Vehicles transporting loads composed entirely of asphalt material are exempt only from the provisions of this section requiring that loads be covered.
3. Vehicles transporting loads composed entirely of petroleum coke material shall not be required to cover their loads if they are loaded using safety procedures, specialized equipment, and a chemical surfactant designed to prevent materials from blowing, spilling, or otherwise escaping from the vehicle.
4. Vehicles transporting loads of aggregate materials shall not be required to cover their loads if the load, where it contacts the sides, front, and back of the cargo container area, remains six inches from the upper edge of the container area, and if the load does not extend, at its peak, above any part of the upper edge of the cargo container area.
5. The requirements of this subdivision shall become operative on September 1, 1990.

1. Any person who provides a location for vehicles to be loaded with any aggregate material or any other material shall provide a location for vehicle operators to comply with this section before entering a highway.
1. A person shall be exempt from the requirements of this subdivision if the location that he or she provides for vehicles to be loaded with the materials described in this subdivision has 100 yards or less between the scale houses where the trucks carrying aggregate material are weighed and the point of egress to a public road.
2. Drivers of vehicles loaded with aggregate material leaving locations exempted from the requirements of this subdivision are authorized to operate on public roads only until they are able to safely cover the load at a site near the location's point of egress to the public road, however, an uncovered vehicle shall not be operated more than 200 yards from the point of egress to the public road.

1. No vehicle transporting garbage, swill, used cans or bottles, waste papers, waste cardboard, ashes, refuse, trash, or rubbish, or any noisome, nauseous, or offensive matter, or anything being transported for disposal or recycling shall be driven or moved upon any highway unless the load is totally covered in a manner that will prevent the load or any part of the load from spilling or falling from the vehicle.
2. Subdivision (a) does not prohibit a rubbish vehicle from being without cover while in the process of acquiring its load if no law, administrative regulation, or local ordinance requires that it be covered in those circumstances.
3. Vehicles transporting wastepaper, waste cardboard, or used cans or bottles, are in compliance with subdivision (a) if appropriate binders including, but not limited to, bands, wires, straps, or netting are used to prevent the load, or any part of the load, from spilling or falling from the vehicle.
4. This section does not apply to any vehicle engaged in transporting wet waste fruit or vegetable matter, or waste products to or from a food processing establishment.