The major factor affecting the west's economic activity is a. forests b. water c. population d. vegetation

The major factor affecting the "West's economic activity" is forests.

Explanation:

According to the US Forest Service data, there are over 84 demarcated regions spread over 13 states in the western United States which are identified as the US National Forests. These States consist of Alaska, Idaho, California, Montana, Wyoming, Arizona, etc. About 8.9 million hectares of the total area of Alaska is covered by forests which is the most in the United States. It is followed by California and Idaho with 8.4 million hectares and 8.3 million hectares of forest areas respectively. These are reserved forests being protected by the US Forest Service. Thus, the presence of these forests is affecting the West's economic activities.