ASPEN Building bridges across the deep Maroon Creek gorge west of Aspen is an exercise in patience - as much today as it was 120 years ago.In 1887, the Colorado Midland Railroad was winning the race with rival Denver and Rio Grande to be the first to reach the lucrative silver mining camp. The Midland's grading crew scratched a roadbed to the edge of Aspen in mid-August of that year, about same time the D&RG reached Glenwood Springs.But the Midland's advantage evaporated when it had to wait for the substantial amount of steel and other materials necessary to build the superstructure of the Maroon Creek Bridge. The D&RG picked an easier route that required smaller bridges across the Roaring Fork River downvalley and avoided the Castle and Maroon creek gorges."Thus, by the middle of September, the Midland had come to the threshold but now had to stand aside and let its rival claim the prize," Malcolm Rohrbough wrote in his book "Aspen: The History of a Silver Mining Town 1879-1893."The D&RG reached Aspen in late October and started service on the line Nov. 2.The Midland's track reached Maroon Creek by December 1887. Once crews received their materials, they slapped together a marvel of a bridge 650 feet long and 90 feet tall in just six weeks, according to the Colorado Department of Transportation's records.The Midland's first train finally rolled into Aspen in early February 1888. The railroad was bankrupt by 1918. The bridge became the property of the Colorado Department of Highways in 1927 and was converted for auto use two years later.Although the trestles and their foundations have taken a beating from weather, rockfall and runoff, the superstructure the Colorado Midland laid down is still in use.Pete Mertes, the project engineer for the Colorado Department of Transportation, marvels at what the Midland accomplished without today's sophisticated equipment. The steel pieces of the bridge were joined by using hot driven rivets rather than bolts and nuts, he said.The old bridge is on the National Register of Historic Places, so it will remain in place even after CDOT's new concrete structure goes up next to it.CDOT started working on the replacement in fall 2005. It will take two and a half years to accomplish what the Midland did in six or so weeks, although a comparison would be grossly unfair.The size is about the only comparable quality of the bridges: "They're light years apart," Mertes said.Federal approvals for the new bridge require painstaking steps to preserve the fragile wetlands and riparian areas in the valley floor. The pier columns had to be in specific areas, for example.The effort to minimize environmental damage dictated the design. The bridge has two massive piers that look like a capital letter A. Pier tables, a sort of hollow box, sit on top of the piers and support the forms for 42 cantilevered segments of concrete that will be the foundation of the traffic lanes.The cantilevered construction reduces the number of piers required."This bridge is unique because of the type of construction required to built it," Mertes said.About 14 of the 42 cantilevered segments, or one third, are complete. BTE/Atkinson JV, the contractor, is casting about one per week now after going through "a learning curve," Mertes said.CDOT is using just one crane in the valley floor to limit environmental disturbance. That also affects the speed of the project.The Midland crews didn't have any constraints based on environmental protections, and they didn't have to worry about disrupting traffic. Mertes said a steel girder bridge design wasn't considered because it would have required traffic delays during construction.This bridge - expected to cost just shy of $14 million - will require 7,500 cubic yards of concrete. For perspective, the average ready-mix truck carries nine cubic yards, so this bridge will require about 833 truckloads.The bridge was originally scheduled for completion in late 2007. Now it looks like it will be late spring or early summer 2008."Challenges with utility relocations, cement shortages and other items have hindered production and may continue to have an impact on the bridge schedule in the future," said CDOT's website for the project.CDOT believes it will be worth the wait. The concrete will last at least as long as the Midland's steel bridge and require less maintenance: "It will last indefinitely if maintained property," Mertes said.The website for the project (www.dot.state.co.us/marooncreek) has details about everything from the old bridge history to the new bridge design.Scott Condon's e-mail address is firstname.lastname@example.org.