The terrain of the Mancos River and Mesa Verde area is illustrated along with the igneous outcroppings as mapped by the National Park Service (black polygons; NPS 2006). The Mancos River Douglas-fir site is located on the north-facing slopes of the igneous outcrop just east of the Park boundary. Select archaeological sites, tree-ring collection sites, and the weather recording station at National Park headquarters are also indicated. DEM datasets for the entire state of Colorado can be accessed at: http://coloradoview.org/cwis438/websites/ColoradoView/Data.php?WebSiteID=15

This view west from the igneous outcrop (foreground) above the Mancos River, Colorado, illustrates some of the recent mortality within the Douglas-fir stand. The northern end of Mesa Verde is located on the horizon (left).

Subfossil Douglas-fir logs are present in various states of decomposition on the rocky talus slopes below the igneous outcrop near the Mancos River, Colorado. The log in the foreground (MAN82) dates from AD 906 (pith) to ±1618, with a ring count after 1580 to the eroded outer edge of the specimen (no sapwood present). The log in the background (MAN80) dates from AD 1345 (pith) to ±1845, with a ring count after 1750. Sapwood is present on MAN80 and the 1845 date is the probable death date of the tree. Preservation has therefore been exceptionally good for over 165 years.

The total ring width measurements for all dated Douglas-fir trees and subfossil logs are plotted from AD 722–2011 (92 radii total). Note the suppression of growth during the severe sustained droughts of the mid-12^th, late-13^th, and late-16^th Centuries. The difference in average growth rates between the subfossil logs and the living trees may largely reflect microsite conditions.

Mean index tree-ring chronologies of EW (a), LW (b), and TRW (c) computed with the Signal Free program (Melvin and Briffa 2008; Cook et al. 2014) for the Douglas-fir trees and logs from the Mancos River site. Decadal versions computed with a smoothing spline (Cook and Peters 1981; same in Figures 8, 9, and 10). The sample size changes over time are also plotted (d).

Correlation coefficients calculated for the period AD 1925–2011 between the monthly moisture balance (P-PE) at the Headquarters weather station, Mesa Verde National Park, and the earlywood (a, gray) and adjusted latewood width chronology (b, dark gray) from Mancos River, Colorado. In both cases the dendroclimatic year begins in April of the year prior to growth and extends through September of the year when these subannual ring components were formed. For the adjusted latewood chronology, note the reduction of correlation with P-PE during the preceding cool season compared with EW and the emergence of a strong current summer signal.

Observed (dashed line) and reconstructed (solid line) P-PE is plotted for the cool (a, September to May) and warm seasons at Mesa Verde (b, June and July). The statistics for the calibration and verification of the reconstructions for both seasons are reported in Table 2.

The EW width chronology was used to reconstruct the cool season moisture balance (P-PE average for September-May) from AD 722–2011 (a), and the adjusted LW chronology was used to reconstruct the early warm-season moisture balance (June-July P-PE) from AD 1030–2011 (b). These two reconstructions are not well correlated at the annual or decadal scale [r  =  0.079 for the annual values (gray) and r  =  0.25 for the 10-year smoothed versions (black) from 1030–2011] and in fact indicate strongly out-of-phase decadal moisture anomalies during the 1460s, 1840s, and 1990s.

Mean ring width index chronologies for four selected collections of Douglas-fir from the Mesa Verde region of southwestern Colorado. Each chronology was computed with the Signal Free program (Melvin and Briffa 2008; Cook et al. 2014). The new data from the Mancos River provide a well-replicated link between the archaeological and living Douglas-fir collections from the region. The correlations between these various overlapping pairs of TRW chronologies are: r  =  0.71 (722–1270), 0.79 (1220–1962), 0.85 (1434–2008), 0.39 (1220–1270), and 0.92 (1434–1962) for Mancos vs. MV archaeo, Mancos vs. Old Tree, Mancos vs. Nash, Old Tree vs. MV archaeo, and Old Tree vs. Nash, respectively.

Mean index chronologies of EW (a), LW (b), and TRW (c) computed using the four collections of Douglas-fir from the Mesa Verde area of southwestern Colorado (the archaeological specimens, Schulman’s old trees, Nash’s living trees, and the Mancos River igneous outcrop, each illustrated in Figure 9). Sample size (d) falls to a few as just two radii before AD 623, and just a single radius from 546 to 553. From AD 1251 to 1400 sample size is not lower than 22 radii.