[3] The ecoregion, also known as a geomorphic province,[4] was unglaciated during the Pleistocene epoch, when it served as a refuge for northern plant species.

shastensis), Pacific silver fir, Weeping spruce (Picea breweriana) and Foxtail pine (Pinus balfouriana).

Remnants of oak savanna, prairie vegetation, and seasonal ponds persist on the mesa tops of the Table Rocks north of Medford.

The region covers 285 square miles (738 km2) in Oregon, in three separate areas around Medford and Ashland, Grants Pass, and Cave Junction.

The wetter foothills flanking the Illinois Valley support Coast douglas-fir, pacific madrone, and California incense-cedar.

Understory species include oceanspray, Western poison-oak, snowberry, Idaho fescue, California brome, roughstalk bluegrass, and ceanothus.

It is drier than the foothills of the Willamette Valley, partly because the summer Pacific high pressure system arrives earlier and remains longer than in ecoregions to the north.

The slopes are covered by Oregon white oak woodland, Coast douglas-fir, grand fir, ponderosa pine, pacific madrone, tanoak, and chinquapin, with an understory chaparral community that includes snowberry, salal, Oregon grape, poison oak, oceanspray, and swordfern.

Many plants have difficulty growing in its serpentine soils due to a shortage of calcium and high levels of magnesium, nickel, and chromium.

As a result, vegetation is often sparse and composed of specialist species that have evolved to grow in the potentially toxic and nutrient-poor serpentine soils.

It supports a mixed conifer forest of Jeffrey pine, tanoak, california incense-cedar, Coast douglas-fir, and montane chaparral composed of manzanita, ceanothus, Idaho fescue, and Lemmon needlegrass.

Historic gold, nickel, chromite, copper, and mercury mining have contributed to water quality problems.

It has a higher fire frequency, less annual precipitation, and longer summer droughts than the Coastal Siskiyous.

The largest of the Klamath Mountains subregions mapped so far, it covers 2,610 square miles (6,760 km2) in Oregon, including public lands within the Rogue River – Siskiyou National Forest.

Productive forests composed of Tanoak, Coast douglas-fir, Coast redwood, bigleaf maple, California laurel, and some Port Orford cedar and Nootka cypress cover its mountainous landscape, with chinqupin, salal, pacific rhododendron, and western swordfern; tanoak is more common than elsewhere in Oregon.

Broadleaf evergreens, such as tanoak and pacific madrone, quickly colonize disturbed areas, making it difficult to regenerate conifer forest growth.

[5] The Klamath River Ridges is characterized by highly dissected mountains, with a dry, continental climate.

Higher altitudes and north-facing slopes have Coast douglas-fir, white fir and red fir; lower elevations and south-facing slopes are covered in ponderosa pine and western juniper, species that are more drought-resistant than other vegetation types found within the region.

[7] The Klamath Subalpine ecoregion is higher, wetter, and colder than surrounding areas, with elevations generally greater than 6,800 feet (2,100 m).

Shasta red fir, mountain hemlock, and some western white pine occur, as well as subalpine meadows with various mixes of shrubs, herbs, and grasses.

Soils tend to be thin and rocky, across various bedrock types including granitics, gabbro, and ultramafic rocks.

The geology is mostly Cambrian through Devonian metasedimentary and minor metavolcanic rocks including metamorphosed conglomerate, sandstone, shale, chert, limestone, and basalt.