Over the course of history, the designated mountains for the tea mountains have either been changed or listed differently. In the Qing dynasty government records for Pu'er (普洱府志), the oldest historically designated mountains were said to be named after six commemorative items left in the mountains by Zhuge Liang, and using the Chinese characters of the native language of the region. These mountains are all located northeast of the Lancang River (Mekong) in relatively close proximity to one another. The mountains' names, in the Standard Chinese character pronunciation are:  Southwest of the river there are also nine lesser known tea mountains, which are isolated by the river. They are:  For various reasons, around the end of the Qing dynasty and at the beginning of the ROC period (the early twentieth century), tea production in these mountains dropped drastically, either due to large forest fires, overharvesting, prohibitive imperial taxes, or general neglect. To revitalize tea production in the area, the Chinese government in 1962 selected a new group of six great tea mountains that were named based on the more important tea-producing mountains at the time, including Youle mountain from the original six. Many other areas of Yunnan also produce pu'er tea. Yunnan prefectures that are major producers of pu'er include Lincang, Dehong, Simao, Xishuangbanna, and Wenshan. Other notable tea mountains famous in Yunnan include among others: Region is but one factor in assessing a pu'er tea, and pu'er from any region of Yunnan is as prized as any from the Six Great Tea Mountains if it meets other criteria, such as being wild growth, hand-processed tea. While Yunnan produces the majority of pu'er, other regions of China, including Hunan and Guangdong, have also produced the tea. The Guangyun Gong cake, for example, although the early productions were composed of pure Yunnan "máochá", after the 60's the cakes featured a blend of Yunnan and Guangdong "máochá", and the most recent production of these cakes contains mostly from the latter. In late 2008, the Chinese government approved a standard declaring pu'er tea as a "product with geographical indications", which would restrict the naming of tea as pu'er to tea produced within specific regions of the Yunnan province. The standard has been disputed, particularly by producers from Guangdong.