the 2,000-foot Northeast Buttress (or the Ellingwood Ledges) on the Crestone Needle (14,197 feet), in Colorado, USA, at grade . 1927 : designs and sells the first rock drill and climbing expansion bolt. 1927 : Joe Stettner and brother, Paul, apply European techniques in the USA on their ascent of the 9-pitch Stettner Ledges (5.7) on the East Face of Long's Peak. 1927 : Fred Pigott experiments with slinging natural chockstones, and later machine nuts, for protection at Clogwyn Du'r Arddu on Snowdon, and led to the modern climbing nut. 1929 : , Demitrio Christomannos, Roberto Perathoner make, in 2 days and placing only 6 pitons, the first ascent of the South Pillar of Marmolada, 5.9+, 600-meters, Dolomites. 1929 : Miriam Underhill and Alice Damesme make the first "manless" ascent of the Aiguille du Grépon, in Chamonix, France. 1930s 1930 : Jack Longland leads, onsight, Javelin Blade at Hollytree Wall, Idwal, at E1 5b (5.10a X) with forty-foot runout at the crux. 1931 : Emilio Comici invents the aid ladder, solid belay anchors, taglining, and hanging bivouacs; tools that changed big wall climbing. He used them all on his 3-day, 57-pitch, 1500-metre climb of the Northwest Face of the Civetta, in the Dolomites, mostly free (5.9+ with 3 aid sections, only 35 pitons). 1931 : Robert Underhill leads the first ascent of the North Ridge of Grand Teton, WY. About 1,500 ft. (5.7) 1932 : and Giuani Rifesser climb Furchetta North Face route, Dolomites, adding a dangerous, 5-pitch direct finish, UIAA VII- (5.10b/c X), only 5 new protection pitons. 1933 : Emilio Comici, Giuseppi Dimai and Angelo Dimai climb, in 3 days, the 1,700-foot North Face Dimai Route of Cima Grande, in the Dolomites, at 5.9 and 3 aid pitches; becomes the world's most overhanging big wall climbing route. 1933 : and Vincenzo Peristi climb the North Face of , in the Dolomites, UIAA VII- (5.10c) (6-pitches). 1934 : Pierre Allain champions bouldering at Fontainebleau; climbs L'Angle Allain, . 1934 : Dick Leonard, Jules Eichorn and Bestor Robinson made the first ascent of the Eichorn Pinnacle, at Cathedral Peak in the Sierra Nevada. 1934 : , Bartolo Sandri climb, in 2 days, the 750-metre South Face of Torre Trieste, Dolomites, UIAA VIII-, maybe the world's first-ever but it's not clear if the crux was done totally free (35-pitches). 1935 : Riccardo Cassin, climb the 700-metre North Face of Cima Ovest,