Geoscience Reference
In-Depth Information
Figure 17-14.
Blue-Bear Lakes vicinity seen from the crest of the Culebra Range looking toward the northeast. The
location of pothole mires within the moraine complex is indicated. For opposite view, see Figure 17-10B. Photo by J.S.
Aber.
Figure 17-15.
Panoramic view of cottongrass mire looking southward; east to right, west to left.
Carex
sp. (sedge)
covers most of the open surface; spruce and aspen surround the fen. E. Volkova stands in water to left side;
photograph by J.S. Aber from a tree on the northern edge of the mire.
droughts (Fig. 17-19). Thus, mire development
and peat accumulation may have been inter-
rupted many times, especially during the middle
Holocene.
mountains; the sedimentary i ll in the San Luis
Valley exceeds 30,000 feet (9000 m) in depth,
and large alluvial fans are built against the
mountain l anks of the valley.
The San Luis Valley of southern Colorado has
been called the highest, largest mountain desert
in North America (Trimble 2001). It is approxi-
mately 160 km (100 miles) long, north-south,
and 80 km wide; elevations span from about
2300 m (7500 feet) toward the central portion to
more than 2500 m (8200 feet) around the
margins. Winter temperature is quite cold (plant
hardiness zone 5; Arbor Day 2006). Because
of surrounding mountain ranges with peaks
exceeding 14,000 feet (4265 m), an extreme rain
17.3.2 San Luis Valley
The San Luis Valley is part of the Rio Grande
rift system, which was active tectonically in par-
ticular during the middle Cenozoic (see Fig.
17-9 and Fig. 17-11). The valley dropped down
along deep faults, while volcanic eruptions
and igneous intrusions took place along the
valley margins. As the valley basement sank,
thick sediment was washed in from adjacent
