Lava Plains

Suggested Citation: Kerr, Andy. 2000. Oregon Desert Guide: 70 Hikes. Seattle: The Mountaineers Books. p. 180.

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The Lava Plains ecoregion is basically a big plateau that has been carved up by the Deschutes, Crooked, and John Day Rivers and other streams. The elevations range from 1,400 to 6,500 feet. Precipitation ranges from 10 to 20 inches annually. There are—and were—very few natural lakes and wetlands, as the source for much of the water affecting the bioregion comes from conifer forests at higher elevations.

Big basin sagebrush and native grasslands were widespread. Seventy-five percent of the former and 80 percent of the latter have been converted to agriculture and urbanization, and much of the remainder is in a degraded state because of livestock and off-road vehicles. Riparian woodland communities were also once common but have been hammered here as they have been everywhere else by dams, irrigation diversions, and so forth.

Western juniper is found in the greatest concentrations and diversity in the Lava Plains. Juniper is associated with thirty different plant communities. Fire suppression and livestock grazing have allowed juniper to expand into sagebrush country.

The unique ash deposits in the Middle John Day country and east of Post are quite diverse and support several endemic plant species. Adjacent to the ash deposits one can often find salt desert scrub types, such as the shadscale and black greasewood communities. The ash deposits came from several sources, but the influence of Mount Mazama (known now as Crater Lake Caldera) ash falls was very significant.

The Oregon Biodiversity Project reminds us to sweat both the large and the small stuff. Consider the arrow-leaf thelypody (Thelypodium eucosmum). Its range is restricted to western juniper communities and is generally adjacent to seasonal springs. This purple-flowered, tall, and showy mustard is found only in Grant and Wheeler Counties, mostly near Mitchell and Kimberly mostly on BLM holdings, and it is threatened by livestock grazing.

The Oregon Biodiversity Project has estimated that 1.9 percent of the ecoregion is adequately protected to conserve and restore biodiversity.