Perhaps I can shed some light on your inquiry. The Penasco
(pen-YAHS-ko)is a small river that starts in the Sacramento Mts. near Cloudcroft NM and flows eastward into the Pecos River near Artesia. Local people refer to the "Upper," "Middle," and "Lower" Penasco. The water in the stream disappears into sinkholes at the east end of the middle Penasco and re-emerges some twelve miles downstream to start the Lower Penasco, and flows on to the Pecos.
Dunken would not be in the Lower Penasco valley, as the terrain and roads branch off at the east end of the middle Penasco and leads southwest to Dunken. The "Lower Penasco Post Office" was located at the HQ of the Bar V Ranch, where Billy Mathews was the first postmaster in 1884. The building is still there, and is used as a barn.
It would be good if you could get hold of my book called "J. B. 'Billy' Mathews: Biography of a Lincoln County Deputy," published by Yucca Tree Press in 1999.
Elvis E. Fleming