150. The "Valley" Radical: 谷
The seven-stroke "valley" radical 谷 is on duty in just one Joyo kanji, the 谷 character itself:
谷 (122: valley)
In this case, the radical name たに works. It corresponds to the Joyo kun-yomi of the 谷 kanji.
If the "valley" radical shifts to the left side of a character, the name たにへん fits. We find 谷 on the left in these kanji:
欲 (987: desire)
谺 (こだま: spirit of a tree), a non-Joyo kanji
Because 谷 is a mere component in 欲, the name たにへん isn't really appropriate, and kanji scholars wouldn't use it, though conceivably laypeople would. That is, radical names are best reserved for the radical that's on duty in a particular kanji.
As for こだま as "spirit of a tree," the Japanese tend to write that as 木霊.
Photo Credit: Christopher Acheson
Etymological Interpretations of 谷
Henshall's newer edition presents various etymologies of the cutely symmetrical 谷:
1. All the diagonal strokes may represent "water flowing," with the 口 symbolizing a "(mountain) spring."
2. The top four strokes might depict "mountain slopes," with the bottom standing for a "valley depression."
3. The top strokes could mean "open up," combining with 口 (mouth, cavity) to yield "wide open mouth" as the overall meaning. If that's true, "mountain valley" appears to be an extended sense, though one researcher posits that "cave from which spring water emerges" is an alternative meaning of 谷.