From the junction with the Baker Mine Trail
, head up a fairly steep draw, and over a saddle towards Milton Mine (1.4 miles). The saddle will greet you with a short segment of singletrack. Mexico is visible in the distance, and your cell phone may welcome you to Mexico.
After Milton Mine, the trail is a well-traveled 4-wheel drive road to the Milton Mine Trailhead (1.6 miles). Here you'll find a tall steel lattice tower with a blue LED flashing light. This tower functions as an emergency call station. Push the red button, and likely US Border Patrol will quickly show up to provide aid.
From here, you can head up the road for a mile to get to the Senita Basin Trailhead.