IOWA ACADEMY OF SCIENCES. 65 



xerophytic openings in which J/in /perns occidentalis var 

 )}unJosperma, small groves of Ficca pioujcns with an under- 

 growth of Rihes ceri'um^ Shephcrdia Canadensis, Ardosta- 

 phylos Ufa-ursi, Junip)en(s coinniunis xav alp/Ha, and Fofen- 

 iilla fruticosa, but the greater portion of the area consists 

 of a rank growth of Artemisia tridenfata and Biqelovia 

 Douglasii. The Giant Lyme grass {Elymus condensafus), 

 Agropj/ron occidenfalis, Sfipa sp., Eriopomim timheUafnni, 

 CnicHs DriinuHondii var acaulescens are common plants. 

 The second flood plain may, therefore, be designated the 

 Juniperus belt. 



The third floor plain is much older than the first and 

 second, and as the chief plant is sage brush, can be desig- 

 nated the Artemisia zone. In this belt the Artemisia 

 reaches its greatest perfection. This area is entirely devoid 

 of trees, and the only shrubs occurring are Artemisia, 

 SijmpJioricarpos and a few Amclanchier and occasionally 

 Bosa Fendleri. The Erio(joni(m umhellatHm, Artemisia, 

 O/iliocarpus, and Stipa are some of the more conspicuous 

 herbaceous plants. The fourth zone occupies the high 

 table lands or benches. The absence of trees, except on 

 the sides of the benches is characteristic. Artemisias are 

 abundant, and also Enrotia lanata. 



On ascending the stream the mesophytic Salix belt con- 

 tinues without interruption, except for the small xeo- 

 phytic parks. The second or Juniperus belt continues 

 up to an altitude of 7,800 feet, where the Juniperus is 

 is replaced by an occasional grove of Piiius Murragana ; 

 aside from this, Artemisia is a predominating type. The 

 third flood plain or Artonisia belt is very much broken up 

 at an altitude of 7,800 to 8,000 feet, forming hills inter- 

 sected with undulating hills and depressions. Picea pun- 

 f/eus and Pin us j\Iurrai/a)ia and Pseudotsur/a occupy por- 

 tions of the hills. The fourth zone is occupied by scat- 

 tered groves of PopnJus tremutoides, Pinus Murrai/ana, and 

 Picea punr/ens, such shrubs as AmelancJtier ahiifolia and 

 Bosa Fendleri. The Arteuiisia is less frequent on the flats 

 and the Eurotia lanata entirely absent. There are, how- 

 ever, extensive belts of Artemisia on the sloping ridges. 



