Packrat (Neotoma spp.) middens from the White Mountains indicate climatic and plant community conditions for the last 19,000 yr. During full-glacial times (ca. 19,000 yr B.P.) and at the Pleistocene/Holocene boundary juniper woodlands were 600 m lower in elevation than at present. Midden assemblages and stable-isotope data suggest lower temperatures and increased precipitation relative to the present into the early Holocene. Two early Holocene middens (ca. 8000 yr B.P.) from lower elevations of the White Mountains contain fragments of pinyon pine and indicate that both pinyon and juniper grew at a site that today supports only a pinyon woodland. Two middle Holocene middens (ca. 5000 yr B.P.) indicate that there was an upward migration of pinyon-juniper woodlands along a high-elevation ecotone, but little change in the middle of the pinyon-juniper woodland. Middens from the late Holocene indicate that present-day plant communities were in place by ca. 2000 yr B.P. or before.

No abstract

The pollen from five packrat middens from the White Mountains region of California were analyzed and compared to previously analyzed macrofossils from the same middens. The middens span the time from ca. 20,000 yr B. P. to the middle Holocene. While there are similarities in the pollen and macrofossil data, there are some subtle differences between the two types of data. The pollen data would support the macrofossil evidence that indicates the arrival of Pinus by the early Holocene. In spite of this general agreement, the pollen evidence suggests that Pinus was not common in the vicinity of the early Holocene midden sites. The results of this study would indicate the importance of using both the macrofossil and pollen evidence from packrat middens.

The use of field classes and the need for university master planning are presented as a way to enhance learning. This fieldoriented, goal-oriented approach to learning is proposed as a general model for university-level geographic education. This approach is presented for physical geography classes, but could also be applied to other subdivisions of geography. Student performance in geographic skills appears to be improved by this approach.

Data from packrat middens are used to reconstruct the migration of singleleaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma) in the White Mountain region of California and Nevada for the last 20,000 years. Today this region is characterized by arid conditions with dry summers. Pinyon woodlands, which are favored by dry summer conditions, are dominant at middle elevations of the White Mountains. The midden record indicates that during the late Pleistocene and early Holocene, juniper was dominant at elevations now occupied by desert shrubs. A late Pleistocene-early Holocene record of desert shrubs was found only in the double rainshadow of the Sierra Nevada and the White Mountains. Pinyon entered the area during the Holocene (ca. 9000 yr B.P.) and subsequently became more important than juniper. During the late Holocene, desert shrubs became established at the lower elevation sites that they now occupy. The late Pleistocene-early Holocene record indicates that there may have been a more zonal upper-level wind flow and associated penetration of Pacific moisture, as indicated by the occurrence of desert shrubs downwind of the north-south-trending mountain ranges. Zonal flow probably became less important during the early Holocene based on the increasing amount of pinyon. The increase in pinyon also may indicate a change from an even seasonal distribution of precipitation to the dry summer conditions presently found in the region. [