What is this helicopter type at a U.S. military base?
In addition to Peter Kämpf's comprehensive answer identifying the helicopter as part of the Mi-17 family, this aircraft is likely to be a Mi-171E, clandestinely operated by the United States government, specifically it is 15-5207. With respect to 15-5207, the pictured aircraft

is a similar colour to 15-5207
has a similar box in front of its engine intakes (possibly for infra-red reduction)
has the same black triangle design around its exhaust
and has a similar proliferation of aerials on its tail boom.


Mi-171E 15-5207 in Springerville AZ, 2016 (source)
15-5207 was photographed at Felker Army Airfield, Virginia USA in December 2017; the orignal picture from Google maps is also Felker (note the provided link does may not show the helicopter depending on where you are). Felker is part of Joint Base Langley–Eustis. This aircraft has been noted at -

Burbank, California 2016
Yuma 2016
Springerville, Arizona 2016
and in 2018 at Opa Locka, Florida.

Understandably, the American military and secret service use of Mi-171E is not widely publicised, although it's known that the CIA has used the Mi-17 in a number of theatres. This particular aircraft carries no identifying markings; it may be connected with the US Army's purchase of 30 Mi-17s in 2013.
The only comment I can find with regard to this particular aircraft is from the Dutch aviation Scramble magazine on social media -

There are rumors that the US Department of Defense are using Russian
build aircraft for Special Forces Operations in areas abroad where no
western type aircraft operate. Evidence of this is very hard to find.
...
It is known that the US Air Force has the 6th Special Operations
Squadron (SOS),based at Hurlburt Field (FL), which is specialized in
Foreign Internal Defense (FID) operations. The primary role of the 6th
SOS is to assess, train, advise and assist foreign aviation forces in
the use of their aircraft, but the squadron also carries out intra
theater support of special operations forces, flying clandestine
night-vision insertion and extraction, air land and air drop resupply
mission with the capability of operating from unimproved runways.


Mi-171E operated by the US Government (source)