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.
First "Ann-in-bikini" cover.
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,..."