Lanzhou folks like their noodles and street stalls, fast food joints and fancy restaurants all sell them. Lanzhou people eat noodles for breakfast and lunch, but not dinner. We ran into this problem when we were there, as we were only able to eat meals in Lanzhou after lunch time because of our tight itinerary, it was difficult for us to track down noodle soup! Our China Odyssey Tours guide informed us that the best and most famous place in Lanzhou to eat noodle soup is Ma Zi Lu. Unfortunately, we were either too far away or it was closed but for whatever reason, both times we ate Lanzhou noodles it was at two different outlets of the same fast-food joint serving the noodles.
No matter where you end up eating Lanzhou noodles (you'll find them in practically every city in China), they are cheap and tasty. We enjoyed ours with nice cold beer and they were the perfect quick-stop meal before we got on our train to Dunhuang and our airplane back to Shanghai, respectively.