234 UNIVERSITY OF COLORADO STUDIES 



Seasonal Aspects. — All of the plant formations show marked changes 

 depending on season. The pre-vernal flora begins to appear about 

 April 15 or May 1. In all except very moist situations Pulsatilla 

 hirsutissima is common while Thlaspi coloradense is even more abundant. 

 These species are found in moderately dense forest, in forest openings 

 and on the open treeless areas of the park. 



Spring may be said to begin May 15, summer about July 1 and 

 autumn September 1 or earlier. Throughout the month of June the 

 flowering plants in blossom are those which at Boulder or Colorado 

 Springs bloom in April and May. Loco weed, Aragallus lamberti, 

 blossoms about July 1 and this is one of the first true summer flowers 

 at lower altitudes. Aspens and willows do not leaf out until late in 

 June. On account of this shortness of growing period it is possible to 

 become well acquainted with the flora in six or eight weeks instead of 

 requiring four or five months as in warm temperate regions. 



Of the different plant formations change of season most affects the 

 appearance of grassland and thicket. Meadow shows, in striking man- 

 ner, rapid changes due to the flowering of many conspicuous species in 

 quick succession. Thus, in the meadow north of Park Lake great 

 differences in the vegetation may be noted even from day to day. 



A careful study of the succession of plants in time of flowering might 

 well be made in one or more associations. Even the student who does 

 not care to make this a special subject of investigation will find interest 

 in noticing, in the meadow zone at East Lake for example, how Pent- 

 stemons give way to Erigerons and these to Campanulas, thus bringing 

 about complete changes in the general aspect of the area. 



The Glaciation of Boulder Park. — It is at once evident from the 

 appearance of the park that its present extent and form are largely 

 due to the action of glaciers. The rounded knolls and shallow basins 

 just east of Tolland which give the rolling character to that part of the 

 park are all of glacial origin. Indeed, to one who has become accus- 

 tomed to the well-drained, non-glaciated stream-cut plains area of 

 Colorado the topographic features here presented seem quite novel. 

 The park is like a small portion of the eastern United States dropped 

 down in the midst of the mountains. 



At some time a terminal moraine, crossing the valley a few hundred 



