We did proceed past that point (despite some very vocal back seat driver telling me not to). The road really doesn't open until June 1st so we didn't expect to reach Silver City-just to see how close we could get. A few miles past the sign the slush got too deep and unpredictable to continue (and the back seat driver may have been threatened with severe, painful punishment if he didn't shut his mouth). We turned around and came home. First stop in town was at the car wash- when we stopped on the way back out of the mountains to go potty we realized there was no way in or out of the Suburban that wouldn't get you filthy dirty. We looked like we'd been four wheeling! Well, we did put the Suburban in 4WD, so maybe, technically we were four wheeling.
We stopped at a big sand pit near the road and the kids went out and climbed the sand mounds (huge sand mounds) and chased lizards for a while. It was a wonderful afternoon! I just wish I'd brought my camera. Next time I'll try to remember it and then post some pictures.