The isotopic composition of soil water used by trees is affected by multiple ecohydrological processes, and the relative abundance of stable isotopes in plant tissue is determined by subseasonal hydroclimatic conditions. We measured δ ¹⁸O in precipitation (δ ¹⁸O _PPT), xylem water (δ ¹⁸O _XW), and cellulose of tree-rings (δ­ ¹⁸O _CELL and δ­ ¹³C _CELL) in dominant and codominant ponderosa pines for the 2015 and 2016 warm seasons during drought conditions. Quantitative wood anatomy, including tracheid lumen diameter (LD) and cell wall thickness (CWT), provided phenological dates of wood formation. False ring formation was measured in multiple trees in response to precipitation from a large remnant storm of Hurricane Dolores that reached southern Nevada . We utilized the opportunity to test if the α-cellulose in false rings had a different isotopic signal between dominant and codominant trees. Indeed, we measured a different isotopic ratio (δ­ ¹⁸O _CELL) in codominant trees associated with higher soil moisture at shallower soil depths. Contrariwise, the δ­ ¹⁸O _CELL in dominant trees formed during the 2016 warm season reflected fluctuations in soil moisture at deeper soil depths, accessing water stored in the macropores of bedrock after a wetter early warm-season and drier monsoon season. No subseasonal differences between codominant and dominant trees were measured in δ­ ¹³C _CELL. Throughout our study, we observed that codominant ponderosa pine tree-ring growth responded to pulses of warm-season precipitation more readily than dominant trees. If southern Nevada continues to trend toward a drier and warmer future, deep soil water recharge will be less reliable and drought stress will threaten dominant trees in old-growth forests.