South Grade Road, also known as Palomar Mountain Road, is a stretch of County Route S6 in the Peninsular Ranges in northern San Diego County, California, USA. It connects Del Mar with Palomar Mountain. The surface is asphalted and it has 21 switchbacks.
This typical mountain road with many curves climbs up to the Palomar Observatory and Hale Telescope, at an elevation of 6,142 ft (1,872 m) above the sea level. The observatory will be closed if travel or other conditions are hazardous. Visitors should be aware that we may close the observatory to the public due to weather or other unforeseen conditions without advance notice. The route was defined in 1959. Watch for fog, fallen rocks on the road, especially during and immediately after rainfall. Travel on Highway 76 & South Grade Road (S-6) may be difficult during and just after rain events. Road closures and rock/mud slides are possible at these times.
The road is certainly breathtaking and it has a fearsome reputation. It has over 20 hairpin turns over the distance of less than 7 mi (11 km). Every year numerous serious accidents are reported, occasionally fatal ones, and far more accidents probably occur that authorities never know about since the bikers would rather suffer quietly than have their insurance companies know what they’ve been up to. This road is usually open all year, but it can be closed anytime when the access is not cleared of snow. Please drive carefully. Winter storms usually mean snow and icy conditions on Palomar generally, in these circumstances, tire chains are required by the Highway Patrol. Again, please drive with caution.