Visa with entrance by land

I am a 55 year old female american citizen. In September I am leaving on a 4 year trip around the world. I do not intend to use air travel on this trip. I anticipate wanting to visit China in early 2015. I would like to have the opportunity to tour china for three months. Could you advise me as to the possibility of doing this, how I would go about getting the appropriate visa, and where I would best enter china. At this point in my trip I will have completed travels in Africa (2013) and Europe and Russia (2014)