<P> The Flatirons on Green Mountain are within the City of Boulder Open Space and Mountain Parks system . They are popular destinations for hikers and rock climbers, with rock grades ranging from easy (5.0) to world - class (5.14 b). </P> <P> Images of the numbered Flatirons on Green Mountain are ubiquitous symbols of the city of Boulder . The area abounds with Flatirons photographs, drawings, paintings, and sculptures . The city government, the University of Colorado, and many businesses make use of this symbol in their logos, advertisements, and marketing materials . Many businesses also use the word Flatirons or Flatiron in their names . In addition, Boulder often is referred to in the tech industry as the "Silicon Flatirons", analogous to Santa Clara Valley's famous nickname . </P> <P> The third Flatiron bore a "CU," for the University of Colorado, in 50 - foot (15 m) white letters from the 1950s until 1980, when the city painted over the initials to restore the natural look of the stone formation . CU students Dale Johnson and Robert Rowlands climbed the flatiron one night in November 1949 to paint the original "C ." The "C" was removed and painted again, with a "U" being added in the 1950s . The letters are still faintly visible under the reddish paint used by the city in 1980 . </P>

Are the flatirons part of the rocky mountains