grant to him from the American
Heart Association provided field expenses for work by Mr. J.R. Alcorn,
collector for The University of Kansas Museum of Natural History, in
1957.

Mr. Harold R. Shepherd of Mancos, Colorado (Senior Game Biologist for
the State of Colorado, Department of Game and Fish), provided advice in
the field, helped in identifying plants, and saved specimens of rodents
(in 1958 and 1959) taken in his studies of the effect of rodents on
browse utilized by deer. Mr. J.D. Hart, Assistant Director of the
Department of Game and Fish, issued a letter of authority to collect in
Colorado; and Superintendent O.W. Carlson approved my appointment as a
collaborator. Mr. "Don" Watson, then Park Archeologist, and Mrs. Jean M.
Pinkley, now Park Archeologist, assisted us in 1956, and since then have
provided advice and assistance, and have reviewed the manuscript of this
report.

Geologically, the Mesa Verde is the northern edge of a Cretaceous,
coal-bearing, sandstone deposit called the Mesaverde group, which dips
beneath the San Juan Basin of New Mexico. An abrupt retreating
escarpment commonly forms on arid plateaus underlain by horizontal rocks
of unequal strength, and characterizes the borders of mesas. Such an
escarpment forms the North Rim of the Mesa Verde. However, the dip of
the rocks has channelled drainage southward and erosion has cut
numerous, deep, parallel-sided canyons rather than a simple, retreating
escarpment. The Mesa Verde therefore is, technically speaking, a cuesta
rather than a mesa. The remnants of the plateau left between the canyons
are also (and again incorrectly in the technical sense) called mesas;
Chapin Mesa and Wetherill Mesa are examples.

Climatically, the Mesa Verde is arid; precipitation averaged 18.41
inches per year for a period of 37 years. Precipitation may be scattered
through the year, and more important, may be erratic from month to month
and from year to year. In addition to low precipitation and periods of
drouth, a great amount of sunshine, and thin, well-drained soils on all
but the more sheltered parts of the Mesa favor vegetation that requires
neither great amounts of, nor a continuous supply of, water.

The vegetation of the Mesa is illustrated in Plates 1 and 2, and
consists predominantly of pinyon pine, _Pinus edulis_ Engelm., and Utah
juniper, _Juniperus osteosperma_ (Torr.) Little. More sheltered areas
along the North Rim and in most of the canyons support