What is the standard of review for appealing against a finding of guilty of conspiring to distribute 1,000 pounds of marijuana?

Silvas contends that the district court erred in finding him guilty of conspiring to distribute 1,000 pounds of marijuana. "[T]he district court's factual determinations [are reviewed] for clear error and its legal interpretations of the Guidelines [are reviewed] de novo." United States v. Castaneda, 9 F.3d 761, 769 (9th Cir.1993), cert. denied, 114 S.Ct. 1564 (1994). Under this standard, an appellate court is "bound to accept a lower court's finding of fact unless [it has] a definite and firm conviction that a mistake has been committed." United States v. Ramos, 923 F.2d 1346, 1356 (9th Cir.1991).