A growing body of evidence demonstrates that ancestral Pueblo people living in the central Mesa Verde region of the U.S. Southwest maintained long-distance contacts with other Pueblo peoples. Questions of Pueblo interactions through time and across space have traditionally been addressed using ceramic sourcing data. This research uses obsidian source data to argue that, from A.D. 600 to 920, residents of the central Mesa Verde region obtained obsidian from throughout the U.S. northern Southwest, but that from A.D. 1060 to 1280 they acquired obsidian almost exclusively from the Jemez Mountains area of north-central New Mexico. In addition, importation of obsidian from the Pajarito Plateau increased during the period of population decline in the Mesa Verde region, and population expansion on the Pajarito. Characteristics of the obsidian assemblage from central Mesa Verde region sites also suggest that Jemez obsidian entered the region primarily in the form of finished arrows, arrow points, and arrow-point preforms. We argue that these patterns reflect return migration by early immigrants from the Mesa Verde region to the northern Rio Grande, an early stage in the development of a migration stream between the two regions.

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Twenty‐seven 14C dates from alluvial deposits and soils exposed in modern arroyos near Zuni Salt Lake, New Mexico, provide evidence for past episodes of piedmont and valley entrenchment by low‐order ephemeral streams. We recognize two episodes of entrenchment at A.D. 900–1050 and A.D. 1300–1400 that correlate to other arroyo‐cutting events in the region. Episodes of piedmont and valley entrenchment are followed by approximately 200–300 years of aggradation until arroyos are filled and shallow flooding with expansive sedimentation returns, completing an alluvial cycle. Many alluvial cycles appear synchronous across much of the southern Colorado Plateau and are likely linked to changes in climate and flood regime. Flooding on small basin drainages near Zuni Salt Lake is related to the Southwest summer monsoon, a meteorological event that is poorly linked to El Niño. Alluvial cycles on small basin drainages affected indigenous floodwater farming by locally lowering water tables and reducing irrigable area during phases of entrenchment and contributed to the aggregation of Puebloan communities on the southern Colorado Plateau in the A.D. 1300s. © 2008 Wiley Periodicals, Inc.