Why do people in Sanmenxia, Henan only speak Mandarin?

The Sanmenxia people you mentioned here can only speak Mandarin, which is a bit general.

People in Sanmenxia should speak Mandarin widely. If you go for a walk in the countryside, there are still many people who speak dialects. Although it is not Henan dialect, it is also called local dialect.

The main point here is that Sanmenxia Dam is the reason why people in Sanmenxia speak more Mandarin. At that time, when the Sanmenxia Dam was built, it was supported by people all over the country, including Beijing, Sichuan, Shanghai, Chongqing and Northeast China. In addition, Sanmenxia is rich in minerals, such as crystal minerals and aluminum minerals. These are the pillar industries of the country, which will gather people from all over the country. If these people speak dialects, they can't communicate. Over time, they formed the habit of speaking Mandarin. Of course, these people worked here for a long time, and then a large number of people settled here. After settling down, including them and their descendants, more people will definitely speak Mandarin. That was a long time ago. Now people in Sanmenxia speak Mandarin.

Therefore, it can only be said that the proportion of people who speak Mandarin in Sanmenxia City is relatively large, and it cannot be said that Sanmenxia people only speak Mandarin.