Now twice so far in my research in Yanqing's history in two different Chinese sources, one in English one in Chinese, I've come across the Shanrong people.
First up was this article, The Economy and Culture of the Shanrong People, from the Beijing Municipal Administration of Cultural Heritage, which doesn't really seem to discuss terribly much about either the economy or the culture of the Shanrong People, but does place them in the Yanqing area making trouble for Yan, Qi and Zhao in the Spring and Autumn and Warring States periods. And then from Baidu Baike we have this very short piece, reproduced in full and badly translated here:
Well, that's not a hell of a lot of information. Wikipedia had nothing and the only articles I can find mentioning these people are all from Chinese sources. Searching Google Scholar only seems to show up people whose given names are Shanrong.山戎族古代北方民族名，又称 北戎 ， 匈奴 的一支。活动地区在今 河北省 北部。见《春秋·庄公三十年》、《汉书·匈奴传上》。后亦为北方少数民族的泛称。
Ancient northern ethnic group's name, also called Beirong, a branch of the Xiongnu/Huns. Active in the northern part of modern Hebei Province. See 《春秋·庄公三十年》、《汉书·匈奴传上》 [I'm not going to try translating the names of these books. Presumably they already have standard English names] Later also a general term for ethnic minorities of the north.
Oddly the character 戎, apart from meaning 'army; military affairs' or being a surname, is also an "ancient name for the tribes in the west".
So who were these mysterious Shanrong people and why are they only mentioned in Chinese sources?
(of course, there is more information in Baidu Baike...)