The rodeo industry makes the most money in July, specifically around the July 4th holiday. The period is called “cowboy Christmas” (or “cowboy’s Christmas”)—when cowboys take home the most money. “Cowboy’s Christmas” has been cited in print since at least 1938.
 
“It was ‘cowboy Christmas,’ the biggest single week of the entire rodeo season” was cited in print in 1958.
 
 
Google News Archive
28 June 1938, Prescott (TX) Evening Courier, “Frontier Days benefit to entire community” (editorial), pg. 4, col. 1:
It is their heyday and sometimes called by the cattle people the “Cowboy’s Christmas.”
   
Google News Archive
11 July 1958, Lewiston (ID) Morning Tribune, “Cowboys Compete In 37 Pro Rodeos,” pg. 8, col. 2:
The western half of the United States spent last weekend whooping it up in the traditional western manner. An estimated 4,500 cowpokes fought it out in 37 professional rodeos in 24 states.
 
It was “cowboy Christmas,” the biggest single week of the entire rodeo season.
 
Google Books
The Cattleman
Volume 64
1977
Pg. 136:
Do you know when “cowboy Christmas” is? Well, according to those fellows who make their living in the rodeo arena, it is the Fourth of July weekend. The Friday/Saturday/Sunday/Monday July 4 celebrations offered a lot of money.
 
New York (NY) Times
Rounding Up an American Tradition
By JUDITH SHULEVITZ; JUDITH SHULEVITZ is a writer who lives in New York
Published: June 18, 1989
COME summer, cowboys and cowgirls hit the trail - the rodeo trail - and the fans are never far behind. Winter is the slow season -a finals competition here, a livestock show there - but in summertime in the West rodeos are as ubiquitous, and as well-loved, as barbecues and county fairs. Pro rodeo riders call the Fourth of July cowboy’s Christmas, because, as David Brown of the Professional Rodeo Cowboys Association says, ‘‘There are so many rodeos to go to they can make a good portion of their income that week.’‘
 
New York (NY) Times
A Sport on the Move, a Rider Who Never Stops
By JOE SPRING
Published: July 5, 2008
(...)
His schedule is most chaotic each year during the week of July 4, known in the rodeo world as Cowboy Christmas.
 
Ruidoso (NM) News
Cowboy Christmas, also known as the rodeo season
By Julie Carter
Posted:  07/05/2013 06:03:34 AM MDT
By the time you read this, America will have just celebrated her 237th birthday. Rodeo cowboys across the country began a week or more ago observing the holiday in their own traditional way called “Cowboy Christmas.”

The summer holiday rodeo season is one of the circuit’s richest weeks of the year with at least 35 professional rodeos and several hundred open rodeos held annually to celebrate America’s independence.
 
policymic
July 23, 2012
On the Rodeo Circuit, July is Cowboy Christmas
Abby Sun in Culture
After graduating from college in May, I grabbed my backpack and, along with Daniel Garber, a friend and former classmate, hopped into a ‘98 Mercury Villager to trail the cowboys and cowgirls who compete in professional rodeos. We arrived just in time for “Cowboy Christmas,” the weeks surrounding the July 4, which earned their name from the numerous professional rodeos held daily throughout the Mountain West.  For rodeo cowboys, Cowboy Christmas is an unparalleled attraction because each contestant has the opportunity to earn payouts of tens or even hundreds of thousands of dollars.