By Greg Kulseth, and D. Tucker July 1, 2011; updated February 6, 2012, and March 20, 2012 with additional information from Bud Hardwick and Greg Kulseth.
Getting there: From I-5 (north or south), take Exit 183 (164th St. SW) and travel east to Meadow Road. Turn left on Meadow Road and travel north to 146th St. SW. Turn right (east) on 146th St. SW and travel about 1000′ to the Martha Lake Airport Park entrance on your right (Snohomish County Park). You can’t miss the rock from the parking lot. But in case you do, the rock is at the edge of the woods to the east, at the NE corner of the soccer field near the covered picnic shelter. Coordinates are N47° 51.888′, W122° 14.182′. There was geocache at this place, I’m not sure if it is still there.
The graffiti that had covered this erratic has been removed by Snohomish County Parks Department, and an interpretive sign about erratics has been installed.
Measurements and details from Bud Hardwick: The erratic is 40′ long, 15′ wide, and 18′ tall. From Bud’s photo and the general appearance of the erratic, the rock appears to be greenstone or greenschist, which is metamorphosed sea floor basalt. This is a common type of erratic found in the lowlands (see other examples of greenstone erratics at Coupeville and Langley, and Lake Stevens.