Broadway—especially the part in Times Square, as it refers to theaters—has many nicknames. Broadway columnist Walter Winchell (1897-1972) frequently called it “the Grandest Canyon.” “Forty-second Street and the Grandest Canyon” was cited in a Winchell newspaper column of September 24, 1929.
   
 
Wikipedia: Broadway (Manhattan)
Broadway /ˈbrɔːdweɪ/ is a road in the U.S. state of New York. Perhaps best known for the portion that runs through the borough of Manhattan in New York City, it actually runs 13 mi (21 km) through Manhattan and 2 mi (3.2 km) through the Bronx, exiting north from the city to run an additional 18 mi (29 km) through the municipalities of Yonkers, Hastings-On-Hudson, Dobbs Ferry, Irvington, and Tarrytown, and terminating north of Sleepy Hollow in Westchester County.
 
Wikipedia: Walter Winchell
Walter Winchell (April 7, 1897 – February 20, 1972) was an American newspaper and radio gossip commentator.
   
24 September 1929, Richmond (VA) Times-Dispatch, “Walter Winchell On Broadway,” pg. 11, col. 3:
Izzy Elinson would have you believe he actually overheard it near Forty-second Street and the Grandest Canyon: ...
 
6 October 1929, Charleston (WV) Gazette, “Broadway Interlude” review by Walter Winchell, pt. 3, pg. 2, col. 8:
Because some of the commentators who chronicle the Grandest Canyon have implied that characters in the tome were based on well-known locals, the authors have breathlessly announced that the report is a triumph in accuracy.
 
Old Fulton NY Post Cards
19 October 1929, Pittsburgh (PA) Courier, sec. 2, pg. 3, col. 6:
THE GRANDEST CANYON
Facts and Figures About Broadway, the World’s Greatest Way
By MAURICE DANCER

27 January 1930, New Castle (PA) News, “‘Sporting Blood’ Proves Good Show,” pg. 13, col. 2:
it should click right merrily along the path to success in what Walter Winchell calls The Grandest Canyon.
 
Google News Archive
19 August 1930, Milwaukee (WI) Sentinel, “Attack by Catholic Theater Group in Gotham Alarms Producers of Broadway Plays” by Dorothy Roe,  pg. 7, col. 7:
The movement, under the auspices of Cardinal Hayes, has aroused wide comment along the grandest canyon since it became known that only two plays in New York were deemed worthy of the “white list” of the Catholic league.
 
Google Books
Esquire
Volume 2, Issues 4-7
1934
Pg. 98:
The nature of their work being especially adapted to concocting clever names for places, they have divided their own “Noo Yawk” into the Stem, the (Main) Drag, the Artery, Maraudway, the Milky Way, the Galaxy, the Gay White Way, the Dirty White Way, the Big or Main Alley, the Grandest Canyon, the Glittering Stem, Mazda Lane, Neon Boulevard, the (Big) Gulch, Gin Gulch, the Noisy Lane, the Street, Wailing Wall Street, the (Grand) Canyon, the Golden Canyon, Hard Times Square, Pokahvenoo, the Roaring Forties, the Naughty Nineties, Mad-hattan, etc., etc.
 
Google News Archive
12 March 1937, Palm Beach (FL) Daily News, “Walter Winchell On Broadway,” pg. 4, col. 2:
Lights That Make Manhattan: (...) The vari-colored fish that romp all over the Wrigley sign at 44th St. and the Grandest Canyon.
 
Google News Archive
28 December 1944, Daytona Beach (FL) Morning Journal, “Broadway Americana” by Walter Winchell, pg. 2, col. 2:
Inhabitants of the Grandest Canyon believe those who don’t live in the Big Town are peasants.
 
Google News Archive
9 March 1945, Daytona Beach (FL) Morning Journal, Walter Winchell column, pg. 4, col. 2:
Along The Grandest Canyon
(Broadway and Tame Square)
 
Google News Archive
24 February 1946, Milwaukee (WI) Sentinel, “Coast to Coast” by Walter Winchell, pg. A10, col. 3:
NEWSSTAND OWNER: It’s a laugh. This Broadway they write about…I’ve been hawkin’ papers here for a dozen years and I ain’t seen nothin’ yet with a surprise in it…The Grandest Canyon, Winchell calls it. Canyon is right! No street’s in a bigger hole.
 
Google News Archive
22 October 1946, Milwaukee (WI) Sentinel, “Coast to Coast” by Walter Winchell, pt. 1, pg. 13, col. 1:
Along the Grandest Canyon
 
Google News Archive
17 June 1952, Milwaukee (WI) Sentinel, “On Broadway: Six More New York Shows Expected to Close Soon” by Walter Winchell, pt. 1, pg. 11, col. 5:
OVERTURE!: The grandest canyon swallowed three more casualties—representing a $280,000 deficit.
 
Google News Archive
26 April 1966, Sarasota (FL) Journal, “Bores And Snobs Crowd Broadway” by Walter Winchell, pg. 9, col. 3:
The glittering billboards have achieve world-wide renown. But it is the people of the Grandest Canyon who are the true expression of its spirit—and the source of its fame.
 
Google News Archive
26 November 1969, Pittsburgh (PA) Post-Gazette, It Happened Last Night” by Earl Wilson, pg. 10, col. 3:
The Broadway Association guarantees the tall buildings in the grandest canyon of them all won’t take away the color and smell of B’way.
 
Google Books
Winchell Exclusive:
“Things that happened to me—and me to them”
By Walter Winchell
Englewood Cliffs, NJ: Prentice-Hall
1975
Pg. 9:
The murder scene was the Metropole, a rendezvous for sports and their ladies on West Forty-third Street—not far from The Grandest Canyon—where the Broadway lights were brightest.