This paper discusses triaxial shear tests conducted on proposed embankment materials for the Oroville Dam, Calif., at unusually high lateral pressures (up to 650 psi) and on unusually large-size specimen (up to 12 in. in diameter). Three general types of material were tested: a naturally occurring clayey sand and gravel; a gravelly to bouldery granular material (coarse dredger tailings) remaining as an end product of the washing and sorting process of hydraulic gold dredging of the late 1800's and early 1900's; and a mixture of the coarse dredger tailings and the fine dredger tailings which were deposited as a residue behind the working dredges and below the water table.