If there's any restrictions it'll be listed in the guide.
As a rule of thumb GPAA claims you can dry wash, but there may be some leased areas or "free use areas" advertised where dy washers are not allowed. A dry washer would not be allowed in the Prescott Mineral Recovery area operated by the Forest Service, but you can pan and dig. Out east, there's no claimable land, but there's some areas listed in the guide that have been leased or offered discounted rates for GPAA members, those may not allow dry washing.
EDIT: I just noticed this said congress. If you mean the Congress group by Wickenburg, yes its allowed. Club rules apply, which basically is common sense like you can't bring a bulldozer to help you out.