Key of C major … that’s a clue …
Well, that’s assuming he’s remembering the correct key. The melody may be right, but the key wrong. Unless you have perfect pitch, it’s quite easy to transpose a melody.
And it looks to me to be more likely to be A minor as given.
Total wild guess, but…‘Love Reign O’er Me’ by The Who? Solo is guitar and violins, I guess.
How about Baba O’Riley?
Excellent guesses gentlemen. 
It is probably a progressive rock song which fits the Moody Blues style. I don’t know - Pavlovs Dog? Nice song anyway https://vimeo.com/37445612
Looking on youtube, there are apparently a lot of instrumental studio versions of their songs out there. But as you say, the only other Moody Blues instrumentals I can think of, such as The Voyage, don’t match the description.
Laguna Sunrise is very close to what I heard. The spanish guitar was not so prominent.
Could it have been part two of Fleetwood Mac’s “Oh Well?”
So it’s a descending set of phrases, each phrase about as long as the one before it and starting one note lower than the previous phrase?
Is the 7th note of each phrase (A, G and E, respectively) longer than the 6 notes that precede it? If not, is there some other reason that you cut the melody line at those points and made 3 lines of the melody?
Approximately how LONG, in duration, is each phrase? Is GFECDEA (for example) a fast-moving sequence like J. Geils band’s “Centerfold” (“my angel is a centerfold”) or Zeppelin’s “Custard Pie” (“give me a piece of your custard pie”) or a medium-fast sequence like Kansas’ “Carry On Wayward Son” (“carry on my wayward son”) or the Doors’ “Light My Fire” (“come on baby light my fire”), or slower like Tom Petty’s “Free Falling” (“she’s a good girl, crazy like elvis”), or what?
Edited to add: is the FIRST note of each sequence longer than the notes to follow? in other word G…FECDEA, F…EDBCDG etc?
“Lick my love pump”?
No wait, that was D minor, the saddest key.
Could it be “quadrophenia” or “overture” or “underture” by The Who.
There are multiple sections in each of those that may fit the bill.
I heard a song on the local radio station a couple years ago and googled the lyrics and got zilch. It was a song I’d heard before several times, could not find the name of it or the band. I came here to SD and eventually it was determined it was done by a local or regional band in the 70’s or 80’s. Odd that there was absolutely nothing to be found online even with some lyrics. I hope you find out what the song is, it is maddening to not know.
Hmmm can’t help you there.
Now, if you had said EGBDF, it would definitely be a Moody Blues song. 
Ok, I’m going to throw a wild guess out there.
Alone Again Or by Love?
Is it the slow part of Questionby the Moody Blues? (starts at 1:40)
Maybe the last minute or so of The Rain Song by Led Zeppelin? That’s what Laguna Sunrise reminds me of.
I’m guessing “Dust in the Wind” by Kansas. There’s a fairly long acoustic guitar/violin part in that song and it is a staple of classic rock.
Don’t know if it’s right but this is an excellent guess!
Yeah, the melody contour kindasortabutnotquite follows the notes listed (although it’s not quite right), and there is an extended version of it that is about 7 minutes long. But only a small portion of it (about a minute or so) is the instrumental interlude. I was wondering if it might be a chord progression like Am-G-E or Am-G-C or something like that.
I’m going to go out on a limb and guess that the OP is intimately familiar with all the extremely well known songs mentioned here.
He said it was a deep track. What most of you are offering up here are not deep tracks. Dust in the Wind: seriously?
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