Alluvium, soil, and overburden are terms frequently used to describe such formations.
Wash. Admin. Code § 173-160-111
Statutory Authority: Chapter 18.104 RCW. 09-01-125 (Order 08-10), § 173-160-111, filed 12/19/08, effective 1/19/09; 06-23-121 (Order 06-08), § 173-160-111, filed 11/21/06, effective 12/22/06; 98-18-104 (Order 98-17), § 173-160-111, filed 9/2/98, effective 10/3/98. Statutory Authority: Chapter 18.104 RCW and RCW 43.21A.080. 98-08-032 (Order 97-08), § 173-160-111, filed 3/23/98, effective 4/23/98.