Final answer:
Bess, formerly known as Sierra, recognizes Old Vernon from her past as the Masked Rider in Oldring's gang of rustlers. Her time with Venters in Surprise Valley helps her to recover and transform beyond the shadow of her previous association with Oldring.
Step-by-step explanation:
The question pertains to the recognition of Old Vernon (Oldring) by Sierra. In 'Riders of the Purple Sage' by Zane Grey, Sierra (Bess) recognizes Old Vernon from her past involvement with him. Old Vernon, also known as Oldring, was a notorious cattle rustler whom Bess knew when she was the Masked Rider in Oldring's gang. Her recognition of Old Vernon comes from her time spent with the rustlers, which is a significant part of her past that she wishes to leave behind, especially after the kindness and love she has experienced with Venters in the isolation of Surprise Valley. Through their shared experiences and Venters' patient care, Bess undergoes a transformation as her health and strength return, and as she begins to separate her identity from her past with Oldring.