Everything is legal...until you get caught!
https://wildlife.ca.gov/Licensing/Suction-Dredge-Permits
Defines for the first time by statute what it means to use vacuum or suction dredge equipment, otherwise known as suction dredging, as the use of a
mechanized or motorized system for removing or assisting in the removal of, or the processing of, material from the bed, bank, or channel of a river, stream, or lake in order to recover minerals; but also clarifying the definition does not apply to, prohibit, or otherwise restrict nonmotorized recreational mining activities, including panning for gold.
Provides the State Water Resources Control Board or the appropriate Regional Water Quality Control Board may take one or more of three specified actions related to suction dredging to protect water quality, including
(1) the adoption of waste discharge requirements or a waiver of such requirements;
(2) specifying certain conditions or areas where the discharge of waste or other adverse impacts on beneficial uses of the waters of the state from the use of vacuum or suction dredge equipment is prohibited; or
(3) prohibit any particular use of, or methods of using, vacuum or suction dredge equipment,
or any portion thereof, to extract minerals based on a determination generally that doing so will cause or contribute to an exceedance of applicable water quality objectives or unreasonably impact beneficial uses; and
Well now.....this is as clear as mud.
A. a mechanical device such as a sluicebox?
B. does the operation cause turbidity?
C. "any portion thereof"

??
I am asking because this law, like most, well all others, especially in CA...is fraught with ambiguities ...
I had a 4" dredge in CA for many years, but when the permits and nonsense started, I just sold it. For me, the laws were NOT on my side, but deliberate vague to allow CA to shut virtually anything down at will.
The fisherman argument always made me laugh...all the time dredging, the fish are all right there, picking at the stuff you stir up...the exposed gravels are much better for the fish eggs, and you create pools for low water fish survival...all good point, but no.....