This postcard shows ski jumping at the "New Steel Slide of the Twin City Ski Club, Minneapolis, Minn." As far as I can determine, this is a 1909 view of the ski jump that was built at Keegan's Lake and held its first tournaments in January 1909.
The following description is from Minneapolis Park History:
Plans were announced December 6, 1908 to build the highest slide in Minnesota two blocks west of Keegan’s Lake in Golden Valley. The slide was planned to be 90-feet tall and cost about $1,000. …The new slide was being built by a new organization, the Twin City Ski Club. What the new club may not have anticipated was that the slide was soon to be on public property — in a Minneapolis park.Another ski jump was built about a year later at Mount Pilgrim by the Minneapolis Ski Club. This was farther north in Golden Valley and according to the Minneapolis Park History was even bigger than the Keagan's Lake slide. That slide apparently was only in use in 1910 and 1911.
On December 27, 1908 the Tribune announced that the club would hold its first competition on January 1 at “Glenwood Park.” The park board was putting the finishing touches on the biggest land acquisition in the history of Minneapolis parks by adding nearly 500 acres, most of it in Golden Valley, to the existing Glenwood Park. The new park included Keegan’s (Wirth) Lake and the Twin City Ski Club’s slide.
Forest and Stream, Volume 76, February 4, 1911 (Google eBook) had an article on Ski Jumping which described the Keegan's Lake ski jump as follows:
To get an idea of the fascination for which this class of sport is known, I visited one of the tournaments held by the Twin City Ski Club in Minneapolis. This club has erected the Glenwood Hill steel scaffold and cable slide, near Keegan's Lake, in the outskirts of the city. In a country where there are no suitable hills for the slide and jumps to be made, it becomes necessary to erect a scaffold from which skiers slide preparatory to the broad jump. The Glenwood Hill scaffold and slide is the highest in the world, and to behold a skier slide the narrow slippery trail, make the famous jump and then land on the steep incline, make a spectacle worth going miles to see. The scaffold consists of a steel tower eighty feet high. From the top leads the slide 130 feet long and pitched at an angle of sixty-five degrees. On top of the scaffold is a platform where the men adjust their skis. The slide and tower are supported by four steel cables and several guy ropes which make the entire structure rigid and free from a swaying motion while the skier makes his descent. The slide is seven feet four inches wide. The cross sections on which snow is placed are composed of hardwood and planks six and eight inches wide and of two thicknesses to prevent the snow from sliding off the structure. The lower end of the slide with a slightly upward turn rests about four feet above the apex of a steep hill, down which the jump is to be made. The incline of the hill is about 150 feet with a pitch equal to that of the steel slide. At the foot of the hill is the "dead man's curve," the lowest point in the valley, and from which the ground takes an upward turn, forming the side of another hill.
It is not clear how long the Keegan's Lake slide was used.