Long strips of land from 5500 to 8000 feet in elevation lying between the plains and the mountains, and filling in with rough hills and valleys the spaces between mountain ranges, comprise a life zone known as the Foothills, and named, by naturalists, the Transition zone. In this zone much of the soil is filled with gravel and weathered rock detritus washed down from higher land or left there by ancient glaciers. Total annual rainfall in this zone is higher than on the plains, and the broken character of the land gives protection from storms.
A greater number of species of flowering plants can be found in this zone than in any other single zone. Local conditions of soil, water and sun exposure vary widely, and these variations offer favorable living conditions to different types of flowering plants and to the numerous shrubs that grow here. Many species of wild flowers which grow on the plains extend into the lower parts of this zone, while other species found in the higher mountains reach down into it, especially along streams.
The chief native trees of this zone are yellow pine and, along streams, narrow leaf cottonwood. Scrub oak covers many hillsides with dense growth, junipers are locally plentiful, and aspens reach down from higher elevations. This tree population attains forest proportions only here and there so that open places for wild flowers are abundant.
In Colorado, visible spring comes earlier in this zone than on the plains below. Sheltered slopes facing the sun pick up the earliest flush of spring green, and by the end of March the very first flowers may here be found in bloom. Late April, May and early June bring the main flower crop. Mass color effects may then be found such as several acres blue with Larkspur, or a whole hillside dotted with red clumps of Lambert’s Loco. The main show is over by mid-July, though asters and sunflower-like composites keep the roadsides colorful till frost.
The picture at the top of this page shows a foothills area near Golden. In good years these hills are rich in flowers by early May. A half hour walk then will frequently yield 30 species or more.
MONTANE
The great mid-sections of our high mountains, lying between 8,000 and 10,000 feet in elevation, make up a life zone called Montane, also known as Canadian. Since most of our Colorado mountains are granite, the typical soils in this zone are granite gravel. Some mountains, however, are faulted blocks of sedimentary rock which have weathered into clay and sand soils. The annual rainfall in this zone is over double that of our plains. This has resulted in forests of lodgepole pine, aspens, and of several species of spruce, with stream banks lined with willows and water birch.
This abundance of vegetation has produced enough humus to build rich black soil in the bottoms of the narrow valleys. In this zone grow a wealth of flowering plants. The principal adverse conditions against which they struggle for existence are: a fairly short season from spring melt to fall freeze; and more tree shade and more competition from tree and shrub roots than they would choose. The steep hillsides in this zone may be quite rock covered. Between the rocks small amounts of good soil may form, and under loose rocks moisture stays for a long time. Trees thrive on these hillsides, but in open spots and beside rocky outcrops flowers get their chance. The columbine grows in perfection in this zone, extending downward into the foothills and upward to timberline.
The building of highways in our mountain areas has introduced new conditions of which some plants are quick to take advantage. The stirred-up soil of new road fills and drainage channel construction will be colorful with fireweed, purple fringe, brown-eyed-susans, with here and there penstemons and asters by the second or third season of their use. Local irrigation accomplished by highway drainage and the use of snowplows, as well as distribution of seeds by animals and even by cars that use the roads, all play their part in this quick restoration of life in the soil that has been torn up.