Prairie- and Sand Hill District. 545 
interest are Corallorhiza multiflora, C. striata, Erigeron subtrinervis, Arnica cordifolia, Calochortus 
Nuttallii, C. Gunnisoni, and Zygadenus elegans ?), 
In north central Colorado, according to RAMALEY this formation is characterized by the 
rock pine Pinus pohderosa var. scopulorum, Juniperus scopulorum is rare. The vegetation in 
general is sparse, probably not over one fourth of the ground surface is covered with plants and 
the light brown and pink of the granite gives color to any near view. The species in the order 
of their abundance are Pentstemon humilis, Geranium Fremontii, Harbouria (Cicuta) trachysperma, 
Sceutellaria Brittoni, Artemisia frigida, A. gnaphaloides, Potentilla glandulosa, Erysimum asper- 
ella (Vesicaria) montana, ertensia lanceolata, Heuchera parviflora 
Opuntia polyacantha (= O. missouriensis) and such shrubs as Ribes pumilum, Jamesia (Edwinia) 
americana, Cercocarpus parvifolius. 
Springbranch- Canyon Formation. This is characteristic of deep canyons 
with precipitous sides and numerous springs. Three types may be recognized, 
viz. linden type, paperbirch type, Pseudotsuga type. 
The Linden-Cedar-Ironwood Association are marked by 7ilia ameri- 
cana, Funiperus virginiana, Ostya virginiana, Fraxinus pubescens (= F. penn- 
sylvanica). One or two facies only may occur on account of the shut-in 
character of the canyon, while on the bluffs all the facies may be present. At 
the base of bluffs and along streams there are thickets composed of Cornus 
asperifolia, C. stolonifera, C. sericea, Amorpha fruticosa, associated with which 
are Sambucus canadensis and Zanthoxylum americanum. 
The canyons with the Paper-birch Association are confined to a narrow 
strip of country on either side of the Niobrara River. The canyons are in- 
variably narrow and precipitous. The facies of this association is Betula 
papyrifera. The individuals are tall and striet and stand above the other trees; 
Funiperus virginiana, Ostrya virginiana, Fraxinus pubescens. Along the upper 
edges of the canyons, the usual thickets of Prunus americana, P. demissa, 
Symphoricarpos occidentalis, Ribes aureum occur. On the shady canyon sides 
grow Elymus strictus, Heuchera hispida, Campanula rotundifolia and Arabıs 
nudicaulis. 
The third type exists in north central Colorado and may be called 
appropriately the “Canyon Forest Formation”. The vegetation extends along 
the stream banks, wherever there is a narrow canyon. The facies consists of 
Pseudotsuga and Salız. 
The secondary species in shady localities are Acer glabrum, Rhus Rydbergii, Populus 
tremuloides, Potentilla fruticosa, Prunus melanocarpa, Physocarpus Torreyi (= Opulaster monogynus), 
Ribes valicola (= R. saxosum), Clematis eriophora, Hydrophyllum Fendleri, Galium trifiorum, 
Smilacina stellata. Growing in more sunny situations are the same pine and junipers, Juniperus 
(Sabina) scopulorum and ]J. sibirica, Symphoricarpus occidentalis, Rhus trilobata, and Ribes pumi- 
lum. The plants immediately along the streams are Populus angustifolia, Alnus tenuifolia (= A. 
incana var. virescens), Mertensia ciliata, Heracleum lanatum, Iris missouriensis and Dodecatheon 
radicatum, 
Allwial Island Formation. The islands are sand-bars which have been 
captured by trees. They exist in all the large rivers of the prairie region. 
1) See Bessev, CHARLES E.: Some characteristics of the foothill Vegetation of western 
Nebraska. American Naturalist XXXH: 111. 
Harshberger, Survey N,-America. 35 
