Technical Abstract: Increased productivity of semiarid western U.S.A. grazing lands is possible with the appropriate plant material combinations. The objective of this study was to compare late summer forage yield of 'Vavilov' Siberian wheatgrass (Agropyron fragile) and 'Mustang' altai wildrye (Leymus angustus) in binary mixtures with two alfalfa's (Medicago sativa) and two forage kochia's (Kochia prostrate) at plant densities of 0.25, 0.5, 0.75, and 1.0 m centers. At the 0.25 plant spacing forage yield of the Vavilov and Mustang monocultures were 1.34 and 1.12 Mg Ha-1, respectively. Mustang-alfalfa mixture yield averages were 11% higher than Mustang monocultures. Vavilov-alfalfa mixture yield averages were 36% higher than Vavilov monocultures, and 45% higher than the Mustang-alfalfa mixtures. Forage yield of grass-forage kochia mixtures ranged from 1.78 to 3.89 Mg Ha-1 at the 1.0 and 0.25 m plant spacing. This represents an increase in forage yield of these mixtures over grass monocultures of 94% at the 1.0 m spacing to over 200% at the 0.25 m spacing. Grass combinations with S-Select forage kochia at all plant spacing were the highest yielding. Although each binary mixture contained equal plants of each species, the contribution of each to overall yield was different. In grass-kochia mixtures, the kochia component averaged 79% of the total yield whereas in the grass-alfalfa mixtures, the alfalfa component of total forage yield varied ranging from 23 to 73% of total forage yield. Rangeland plantings that include forage kochia or a legume such as alfalfa may increase productivity, especially with forage kochia.