"A reported mineral occurrence located in sec. 6, T20N, R14W, MDM, 7.1 km (4.4 miles) NNW of Longvale and 5.4 miles S of Laytonville on highway 101, on land of undetermined ownership. NOTE: MRDS database stated accuracy for this locality is 5,000 meters."
The Mindatsymbol on the "hybrid map" is only 500 meters away from the TL for howieite, deerite and zussmanite, the Laytonville Quarry: that is the bleuish-gray spot beside the highway in the direction "ten o'clock'. Also the description of the 3 minerals is the same as they occur in the Laytonville Quarry.
Given the possible error of 5000 meters in the coordinates and the similarities in the description, I suppose this occurence to be the same as the Laytonville Quarry (or at least an outcrop of the same unity a few 100s of meters away)