I'll assume "ca" refers to California rather than Canada. Maryland is about 200 miles across which leaves a lot of possible halfway points. I'm not sure that matters. The bulk of them will be in the center of the country, in places like Yukon, Oklahoma, which is about as far from any coastal beaches as it is possible to get.
Stuart, CA.
Encino, CA
Cherokee Mobile Gardens, California.
Whitehall, Montana, between Bozeman and Butte.
Rochester, CA is a halfway point between LA and Victorville.
halfway points
The halfway point between Kingman, AZ and Sacramento, CA falls in or around Keene, CA.
The halfway points are the points which mark the half distance covered by the flight. These lie in the mid of both the above mentioned places. These points change for different locations. Halfway points for the above mentioned places are Richmond or Berkeley CA.
Del Mar or Solana Beach look pretty good...
It is 2,707.41 miles according to MapQuest.
Kettleman City, CA
Assuming you take U.S. Higway 101, Greenfield, CA is halfway between Paso Robles, CA and Hollister CA?