Add a Feature to a Layer by Using the Difference of Another Layer - Basic

[ClackamasCrime_Analysis]

I have a polygon layer of our county's land areas, but I also need to add a huge, two part chunk to this layer (U.S. Forest Service land) that lies within our county that is currnetly not part of my polygon land area layer.

I have both the land area layer AND the county border layer and need to get the two gray chunks to become a single feature added to my land area layer. What tool, or process can I use to do this? I have the Basic Edition of ArcPro, and don't have the resources unfortunately through my agency to go above that. 

Attached is a screenshot of both involved layers stacked, showing the gray area of the whole county layer that I need added as a feature to the land area layer on top of it. 

I am so stuck, please, anything helps!

Ashley 

[Sean_Wray]

If I understand what you want to do, it sounds like the Union tool should work. Computes a geometric union of the input features. All features and their attributes will be written to the output feature class.

https://desktop.arcgis.com/en/arcmap/10.3/tools/analysis-toolbox/union.htm

[DanPatterson]

Analysis toolbox licensing—ArcGIS Pro | Documentation will elaborate on your licensing issues

Union, plus others will all work to some degree, but you will have to delete duplicate geometries that result from the combination process.  You could even try a pairwise erase (left side of the map) then a merge of the result with the unpopulated portion to the right of your map