Llano Estacado Caprock Escarpment and Breaks Shrubland and Steppe

Geology

May occur on various surfaces that are sufficiently resistant to erosion to form breaks or escarpments. This includes sedimentary deposits such as sandstones, limestones, or shales, or less frequently, igneous formations such as basalt. Breaks associated with the Permian Blaine Formation may have gypsum exposed or influencing the vegetation.

Landform

Breaks and escarpments including slopes and nearby uplands, sometimes associated with canyons or drainages, but not necessarily. The system occupies slopes, but may continue over transitions to more level sites upslope and downslope.

Soils

May occur on various soils, as well as on sites where little soil development has occurred. Rough Breaks Ecological Sites are characteristic of this system, but other sites such as Rocky Hill, Shallow, and Gravelly Ecological Sites may also be occupied by this system.

Parent Description

This system is closely related to, and may overlap with the previously described system Southwestern Great Plains Canyon System (CES303.664), though the currently considered system is not confined strictly to canyons. The physiognomic character of occurrences ranges from sparsely vegetated to shrubland, to sparse woodland. Bare ground is often conspicuous and herbaceous cover is usually dominated by mid- to shortgrasses such as Aristida purpurea (purple threeawn), Bouteloua curtipendula (sideoats grama), Bothriochloa laguroides ssp. torreyana (silver bluestem), Bouteloua gracilis (blue grama), Bouteloua hirsuta (hairy grama), and Schizachyrium scoparium (little bluestem). Forbs, including species such as Artemisia ludoviciana (western mugwort), Thelesperma filifolium (slender greenthread), Calylophus spp. (sundrops), Chaetopappa ericoides (heath least-daisy), Krameria lanceolata (trailing ratany), Zinnia grandiflora (plains zinnia), and Melampodium leucanthum (plains blackfoot), may also be present. Shrub canopy may be dense, with some species reaching tree stature, and on some sites forming sparse woodland. Shrub and tree species include Juniperus pinchotii (redberry juniper), Juniperus ashei (Ashe juniper), Prosopis glandulosa (honey mesquite), Rhus trilobata (skunkbush sumac), Rhus microphylla (littleleaf sumac), Dalea formosa (feather dalea), Ziziphus obtusifolia (lotebush), Ephedra antisyphilitica (joint-fir), Artemisia filifolia (sand sage), Mahonia trifoliolata (agarito), Cercocarpus montanus (true mountain mahogany), Quercus mohriana (Mohr's shin oak), and Gutierrezia sarothrae (broom snakeweed). Occurrences over gypsiferous formations (such as the Permian Blaine Formation) are mapped separately, though they are compositionally very similar to the typical type. Some species that may suggest the presence of gypsum influence include Nama stevensii (Stevens' fiddleleaf), Calylophus berlandieri (Berlandier's evening primrose), Phacelia integrifolia (gyp phacelia), Thelesperma megapotamicum (Navajo tea), and Haploesthes greggii (false broomweed), but these species may or may not be present at all sites. The gyp breaks tend to have sparser shrub canopy, reduced herbaceous cover, and more visible bare ground, sometimes with exposed gypsum strata visible.