Scan & some info supplied by Al Dellinges thanks to Henry R. Kujawa's report to GCD error list.
The on-sale date is from the publication date recorded in the Catalog of Copyright Entries, Part 2, Periodicals, 1940, New Series, Vol. 35, No. 3.
The story title is taken from the cover blurb.
first line: "A search for the lost valley into whose depths many an adventurer has vanished,..."