This route follows a blocky bent line that rises in a continuous sweep from the unnamed glacier shared by Early Morning Spire and Dorado Needle to the 8440 foot summit.
The route starts in Marble Creek cirque, which is secluded from easy access by steep ridges, trailless valleys, and numerous glaciers. As such it presents a long approach from the nearest trailheads off of the Cascade River Road and can be counted on for a lonely climb. See Selected Climbs in the Cascades Volume II for the entertaining story of the first ascent.
The buttress itself offers over 1000 feet of quality technical climbing featuring steep cracks and slabs, photogenic gendarmes, and airy knife-edge traverses. Outstanding views of Eldorado and the Triad abound, while countless North Cascade and Olympic summits can be seen in the distance.
The routes of Marble Creek cirque present difficult access due to the aforementioned valleys, ridges, and glaciers. The two most practical points of access both traverse from Eldorado Peak, which conveniently has easy trails leading to its upper slopes.
There are two common ways to get to the Eldorado Glacier and upper reaches of Eldorado Peak. One is via Eldorado and Roush Creeks. To make your way up Eldorado Creek, follow the colorful directions given on the Eldorado Peak main page to the Eldorado Glacier.
The other way to Eldorado Glacier is to drive to the end of Sibley Creek Road and traverse the northern slope of Roush Creek. This option is recommended by Jim Nelson in Selected Climbs of the Cascades, and by personal acquaintances for those proceeding to Triad Col.
Once at the edge of the Eldorado Glacier two more options present themselves:
One option is to make your way to Triad Col on the Southwest side of Eldorado Peak via either hike in. From here drop down onto the Triad Glacier and traverse across other small glaciers, snow, and talus to the basin between Early Morning Spire and Eldorado Peak. See the West Ridge route page of Eldorado Peak for more details.
The other option is more circuitous, but probably more straightforward. From the Eldorado Glacier climb to the East side of Eldorado Peak and around the East Ridge of that summit onto the Inspiration Glacier. Traverse generally North across the Inspiration Glacier to the 8000-foot Inspiration-McAllister Glacier col and continue Northwest downhill across the McAllister Glacier. Travel to the lowest gap on the Southwest side of the glacier, the Marble Creek-McAllister pass at 7600 feet, and find a manageable crossing to the small glacier on the Marble Creek side of the pass. This will generally be on the Easternmost side of the pass. From here, descend the lightly-crevassed ice to Marble Creek cirque.
At least two parties have done this climb car-to-car in a day, but the distance involved dictates at least two days for most parties.
The most common and easiest descent route will be via the Northwest Ridge and McAllister Glacier so any camps would be best placed between that descent route and the route back to the trailhead.
The Southwest Buttress of Dorado Needle can be reached by ascending a prominent gully, often snow-filled year-round, from about 700 vertical feet below the Marble Creek-McAllister pass to the base of the objective.
From the prominent snow-filled gully connecting the small unnamed glacier spilling South from Marble Creek-McAllister Pass to the unnamed glacier between Dorado Needle and Early Morning Spire ascend to the blocky toe at the lowest point of the buttress. This is to climber's left of the uppermost portion of the gully which terminates in a dark and wide chimney.
The cleanest and most reasonable climbing follows a left-leaning, right-facing corner up good cracks where the low-angle terrain at the toe becomes distinctly steeper. This corner can be followed climber's left for about 90 meters to lower-angled terrain leading up and climber's right. 100 meters of alternately blocky and slabby low to mid fifth climbing leads to the top of a prominent low-angle slab nearing the edge of a large gully cutting up and climber's left to a notch in the buttress crest.
Reasonable blocky low fifth class climbing veers climber's left from the top of the slab almost to the buttress crest on the left-hand skyline. 60 meters of steeper corners takes one to the buttress crest from here.
The crest is followed for 200 increasingly airy meters around small towers, up steeper slabs, and through shallow notches to the final summit headwall. Relatively clean climbing is found following a prominent gully slightly climber's left to potentially some steeper cracks and eventually the Northwest Ridge, which is finished to the summit over more low-fifth blocky climbing.
Rock rack to 2", ice axe, crampons, rope at least 50m long.
Descend the Northwest Ridge route per the description on the Northwest Ridge route page.