Scablands
from https://www1.usgs.gov/csas/nvcs/unitDetails/860590
"Artemisia rigida is restricted to the Columbia Plateau scablands with shallow, poorly drained, lithic soil over fractured basalt that is often saturated in winter, but typically dries out completely to bedrock by midsummer. "
The main USDA soil-type designations are Argabak (the shallowest) and Bakeoven. Though the user interface is a little cranky, interactive soil type maps with a lot of associated information can be found at https://casoilresource.lawr.ucdavis.edu/gmap/. You have to zoom in far enough to make the boundaries visible.
The area can't be bounded by one rectangle, but this iNaturalist view includes a lot of scabland around Whiskey Dick ridge:
https://www.inaturalist.org/observations?nelat=47.056751100429274&nelng=-120.06335303653032&place_id=any&swlat=46.96357893443272&swlng=-120.28582618106157&view=species&iconic_taxa=Plantae
Another area that has lots of readily accessed (but under-observed) scabland on top of small benches is Babcock Bench, just to the east of the Columbia river:
https://www.inaturalist.org/observations?iconic_taxa=Plantae&nelat=47.19647291927723&nelng=-119.98099849093705&place_id=any&subview=map&swlat=47.17214757595927&swlng=-120.00254199374467
The famous channeled scablands are south of Grand Coulee dam, in the old Columbia river drainage.
Scablands (as used here, not identical to channeled scablands) are common in Kittitas and Yakima Counties, and there are also many patches to the north in Chelan County and east and northeast in Douglas and Grant Counties on the east side of the Columbia River. They are defined here as shallow rocky soils (less than 40 cm deep) over basalt bedrock from the Columbia Plateau basalt flows. The easily recognized Pediocactus nigrispinus is a good indicator in some areas, but it is not always present or may be sparse and hard to find. With a little experience, Artemisia rigida (Scabland Sagebrush) is easier to pick out and it seems to be present in all but the rockiest spots. If you see a sizeable area with rocky soil and sparse vegetation but lots of a low winter-deciduous sagebrush (no more than 3 feet tall) it is very likely Artemisia rigida. They also almost always have abundant small bunch grass Poa secunda, but this isn't as easy to recognize and is found in other areas as well. The scabland areas are often nearly flat or on gentle slopes, making them easily accessible and most are on very poor farm/range land so they tend to be public and unfenced. In some places they sit on top of obvious basalt benches (rather like very short mesas with a basalt escarpment around the edges). The widespread much taller Artemisia tridentata (Big Sagebrush) does not grow on scabland soils but is usually present in adjacent deeper soils.
The scablands support a remarkable diversity of plants, but all the plants are low growing and often early plants have died back before later plants flower so they never appear lush. By midsummer all but the Artemisia rigida and the Eriogonum subshrubs and the cacti have died back, so they look even more barren. For a few precious weeks in early to mid spring the are lots of flowers. April and early May are peak flower times, but there are a few Lomatiums that flower in March as well, and a few plants still in flower through mid June. In some patches (mostly in Kittitas County), the endemic Lomatium quintuplex is abundant and produces a sparse carpet of small yellow flowers peaking usually in April and early May. Following warm winters (typically El Nino years) all of the flowering times are a few weeks earlier.
Common associates in Kittitas County scablands and less fully explored areas in Chelan and Douglas Counties to the north (associates in Yakima County just to the south are probably very similar but I have not visited them as much):
Allium acuminatum
Astragalus purshii
Antennaria dimorpha
Balsamorhiza hookeri
Castilleja thompsonii
Delphinium nuttallianum
[Draba verna, not native]
Eremogone franklinii
Erigeron linearis
Erigeron poliospermus
Eriogonum douglasii
Eriogonum thymoides
Lewisia rediviva
Lomatium canbyi
Lomatium farinosa
Lomatium gormanii
Lomatium macrocarpum
Lomatium quintuplex
Lupinus sp. (probably L. saxosus)
Neoholmgrenia hilgardii
Nestotus stenophyllus
Nothocalais troximoides
Pediocactus nigrispinus
Penstemon gairdneri
Phacelia linearis
Phlox douglasii
Phlox hoodii
Phlox longifolia
Phoenicaulis cheiranthoides
Poa secunda
Trifolium macrocephalum
Viola trinervata
There are less common associates, and be aware that this list does not include plants of deeper soils adjacent to many of the scabland expanses, which support a quite different plant community associated with Big Sagebrush. For scabland, look for areas that are rather barren looking and with obviously rocky soil, lacking any tall shrubs, and usually with lots of the low rather scraggly looking Artemisia rigida (which is also deciduous if you are there from about November to March). Often the Big Sagebrush will be in lower areas or mounds of deeper soil, with the scabland mostly on ridges, slopes (low rounded ridges, don't expect mountains), and benches. There may be interspersed talus slopes or rocky ridge tops, which tend to support even fewer plants.
The delineation between scabland and Big Sagebrush habitat is often rather abrupt but sometimes they are intergraded or occur in interspersed patches.
