Predawn and midday plant water potential measurements, collected on terminal twigs using a scholander-type pressure chamber (PMS Instruments, Corvallis, OR, USA). Measurements were collected from 1-3 canopy dominant or co-dominant raments in 12 mature trembling aspen (Populus tremuloides) near aspen's low elevation range edge in the San Juan National Forest in southwest Colorado, USA. Clones were either growing on north-facing (n=4) or south-facing slopes (n=8) and had either grassy understories (n=6) or shrubby understories dominated by Symphiocarpus albus (n=6). Measurements were collected in the early growing season (2010-06-23), in the mid growing season but prior to the onset of the summer monsoon (2010-07-16) or in the late growing season after the onset of the monsoon (2010-08-17). Data are published using the PSINet data submission template (https://psinetrcn.github.io/). This data is a portion of the data analyzed in: Anderegg LDL, Anderegg WRL, Abatzoglou J, Hausladen AM, Berry JA. 2013. Drought characteristics’ role in widespread aspen forest mortality across Colorado, USA. Global Change Biology 19: 1526–1537.