I stumbled across the website of Rolf Gross, which has an incredible selection of photo-diaries, travel writing, and assorted essays. What caught my interest particularly was his description of a visit to Lanzhou in 1983.
The first photo on the page is of a sick child being wheeled along on a pushcart, with a mosque in the background. At first glance, I was pretty sure that I knew which mosque it was: the Shuǐshàng Qīngzhēnsì (水上清真寺), or 'Waterside Mosque', on Běi Bīnhé Lù (北滨河路), near Zhongshan Bridge. We confirmed this through a short correspondence, and by cross-referencing Rolf's route that day (along the north bank of the river upstream from Zhongshan Bridge) to another online photo.
Rolf has given me permission to republish his photo here. The photo was taken facing west, which means Rolf was standing midway between Zhongshan Bridge and the mosque.