C.L. Pond's 1870 photo of backside of snowshed at Donner Summit
The uphill-bound wagons and (after 1901) cars and trucks came into the snowshed after climbing the steep incline, made a sharp 90-degree turn inside the shed, and made their way through this opening and continued toward the camera on the raised road. Only the road's supporting rocks can be seen in this photo. Imagine the potential problems with two wagons or cars inside at the same time moving in opposite directions, with a train coming. Yet this was how it was for 48 years, from 1867 until August 1914, when the under-the-railroad "subway" was completed 100 yards to the east. More about that on the Historical Photos page.
Below is another photo I recently discovered, this one by Anthony Bros, which shows both sides of the road passing through the tunnel. Notice the rock outcropping that the road made it's way around on the south side of the tunnel (left side in this photo). Surprising that they didn't blast that away after all the blasting they did for the tunnel. The photographer for this photo was on the same spot as the 1992 video photographer--only turned around.
Below is a detail from a Bierstadt 1872 painting showing the opening from the "front" side, climbing up to the summit, and the road after it leaves the snowshed, curving around the outcropping.