This Sunday thousands of ganja enthusiasts will gather in Denver's Civic Center for what has become an annual rite of spring, the embrace of cannabis culture at 4:20 on 4/20. But this weekend also marks the peculiar collision of several more somber anniversaries, commemorating some of the worst days this part of the country has ever seen. "April is the cruellest month," T.S. Eliot wrote in the opening line of The Waste Land, "breeding lilacs out of the dead land, mixing memory and desire." And some of the memories of April 20th in Colorado aren't exactly blissful.