1. Important slides for PBL

2. The Ziegler reservoir site is located in the Elk Mountains of western Colorado, near the town of Snowmass Village. This is an aerial view of Ziegler Reservoir looking south toward the snowmass ski area.
The Ziegler basin is in a very unique topographic setting, perched on top of a ridge at an elevation of 2705m, and the basin is enclosed by a glacial moraine, deposited during the Bull Lake Glacial period more than 140,000 yrs ago.
The basins topographic setting is ideal for plant macrofossil work, because the drainage area of the basin is very small and only comprised by the inner slopes of the surrounding moraine. So, any plant materials being washed into the basin sediments are likely going to be derived from local vegetation surrounding the site, and we can be confident that fossil plant remains from the paleolake and wetland deposits were also derived from local plant communities growing in close proximity to the site.
2705 m

3. Present-Day Plant Elevation Ranges
The upper panel in this figure is a generalized illustration of the vegetation zones along a transect from Glenwood Springs, CO along the CO river up to The Ziegler Reservoir site. You can see that Ziegler Reservoir lies at an elevation where Spruce-fir forest and Mixed conifer, aspen and oak shrubland communities intermix. And the character of this boundary between zones is not abrupt, it is actually very heterogenous and patchy where the vegetation is highly controlled by slope aspect and substrate, as we see so dramatically around Ziegler reservoir with very different vegetation on north and south slopes.
The lower panel shows the elevation ranges of the major tree species occuring in the region, in relation to the elevation of the Ziegler site at 2705 m. The Ziegler site presently sits at the lower elevational limit of Abies lasiocarpa which is the only conifer at the site today, and the upper elevational limit of Quercus gambelii, and well within the range of the mixed conifer forest taxa Populus, Pseudotsuga, Picea.
These two taxa in blue, Abies concolor and Pinus flexilis are two taxa that can occur at the elevation of the site, but they don’t appear to be in the Snowmass area today, but they do occur in other areas of Colorado, A. concolor is found in the southern part of the state at lower elev. And P. flexilis is typically found at higher elevations.
Data from Hartmann et al., Rocky Mountain Herbarium

4. Ziegler Plant Macrofossil Record
90 Taxa, 54 Genera, 36 Families
Our analysis of the Ziegler macrofossil record resulted in the identification of
90 different taxa representing 54 genera and 36 plant Families. The plant remains were derived from aquatic and wetland plants, coniferous trees, deciduous trees and shrubs, as well as herbaceous plants.
Aquatic and wetland plants
Coniferous trees
Deciduous trees and shrubs
Herbaceous plants

5. This is a stratigraphic diagram for the site showing the Ziegler reservoir sediment record which is composed of 18 units, from the bedrock at the bottom to 18 at the top.
Here is the peat pit locality which samples units 18 thru 15, however only units 16 and 15 were processed for macrofossils, so our youngest samples are about 77ka.
Here is the location of the twisty trench which covers Units 16 thru the top of Unit 8, from 77ka to 109ka
Locality 88, which sampled an exposure of the main silt correlates with unit 8.
Lastly, the bulk samples were collected from this area during the bone excavation and the samples span from the beach silt correlated withy Unit 13 down thru the oldest lake sediments of the basement silt of units 4, 5 and 6, samples may be as old as 138ka.

6. Composite Stratigraphic Section
77.2 ka
MIS 5a
MIS 5b-a
MIS 5c-b
~60 kyr of lake and wetland history
MIS 5c
This is a Composite stratigraphic section showing how the measured sections and the bulk samples overlap each other, giving us a continuous record from Unit 4 thru Unit 16, with the record beginning about 138ka in late Marine Isotope Stage 6, through MIS5 substages 5e-d-c-and b…into MIS5a where our macrofossil record ends about 77.2ka. This is a very unique record, which captures about 60ka yrs of lake and wetland history, and there are no other terrestrial records in western North America that cover the entire length of the last interglacial, capturing all of MIS5, as this record does.
MIS 5d-c
MIS 5e-d
Late MIS 6-5e
138.5 ka

7. Elevational Ranges of Modern and Fossil Plant Taxa
Elevation (m)
To understand the habitat preferences of these fossil taxa a little better we plotted their elevational ranges and compared them to the elevation of the Ziegler site.
This figure shows plants found in both the modern vegetation and fossil record in the first box, the second box shows taxa likely to occur in the modern veg near snowmass but they were not id’d in our surveys. You can see that the elevation of the Ziegler site fits within the elevational ranges of these fossil taxa.
We also have plant taxa that are only found as fossils, which tend to presently grow at elevations higher or lower than the Ziegler site, and some have there upper elevational limits near the elevation of Ziegler. 9 of these taxa are presently found within CO and one taxon is not recorded as living within the state.
Modern and Fossil Taxa
(in veg surveys)
Modern and Fossil Taxa
(not in veg. surveys but likely living nearby)
Within CO
Outside CO
Fossil Only
Extra-local taxa
at lower elevations

8. Alpine peatland (fen), conifers only, cooler than present MIS 5a
No trees, cooler than present during MIS 5b
Montane mixed-conifer forest
Warm like the present, or warmer
late MIS 6 to 5c
This is a condensed version of the macrofossil record for Ziegler Reservoir. The red dots are the taxa that do not occur at the site today and tend to occur at lower elevations. And the blue dot is Pinus flexilis that tends to occur at higher elevations. The record begins in the basement silt with presence of coniferous, deciduous trees a few herb taxa and some aquatics, as we move up the section into units 7 and 8 the diversity in the deciduous taxa and herb taxa increases and we see more abundant lower elevation plants like A. concolor. We also see an abundance of oak which prefers drier and warmer climates. Missing data from unit 9. units have a similar flora of conifers, deciduous, herbs and wetland plants only a little less diverse.
In unit 14 we see a significant change and there are no tree taxa present in the macrofossil record. And very few herb and aquatic taxa. Moving up into units 15 and 16 of the peat, we have a return of conifers but no deciduous taxa, with a few herbs and some aquatics and an abudance of moss.
So the record can be divided into 3 zones. With the lower zone suggesting the presence of a montane mixed conifer forest with oak shrubland very similar to the veg at the site today. And the next zone has no tree taxa, possilbly indicating a cooler than present climate, and finally the upper most zone represents an alpine peatland or fen, with an abundance of moss, conifers only and possibly a cooler than present climate.

9. Conclusions
Shallow water environments with alkaline and hardwater conditions existed in Ziegler Reservoir throughout the history of the lake, suggesting that groundwater percolating through calcareous bedrock or soil was an important water source.
MIS 6 - 5c: Macrofossils suggest a mixed montane forest environment was present, similar to today, but including some lower elevation plant taxa (Abies concolor and many herbs) suggesting that the climate was as warm or warmer than today.
MIS 5d: There is a treeless period, with a climate cooler than today.
MIS 5a: A peatland (fen) occupied the basin, and conifer taxa Picea sp. and Pinus flexilis were present, deciduous trees were absent, and the climate may have been cooler than today.
Overall, the climate and vegetation of the Last Interglacial were not largely different from today, even though these two interglacials are separated in time by a glacial period with very different climate and vegetation.