There is a turnout 2.3mi's NW of Quail Springs picnic area along the main road through Joshua Tree NP.  The turnout is on the right side of the road and appears to have no reason for being there.  Samuelson's Rocks are 233deg heading from the turnout, a short 1.3mi walk across essentially flat desert floor terrain. 

Click the "eye" to see a 3D terrain model view from the location of the eye icon, looking in the direction of the blue arrow.