Pick up the Inter-American Hwy/Ruta 5 at the coastal town of Chañaral. Continue south for 91 km until you veer onto the C-302 at Bahía Inglesa. At or just before Puerto Viejo, merge onto the C-324 to continue your southward push for 109 km until you reach Carrizal Bajo where you’ll find provisions. Leave Carrizal Bajo riding south on C-470. Huasco Bajo, which is just off the coast, is 51 km to the south and Huasco proper is a further kilometer or two from there. Be aware that the C-470, which runs pretty close to the sea coast, has several offshoots that allow you to detour even closer to the waves and spume. While all of this is technically unpaved, it is for the most part extremely hard packed and, if memory serves, rarely sandy.
From Huasco you can take the C-46 east to Vallenar where you’ll find a petrol station and from there continue south to veer back to the coast on the C-500. Alternatively, the C-494 leaves Freirina going south for 74 km and from there you can meet up with the C-500 for the final 40 km to Chañaral de Aceituno where there are restaurants, hostels, and beach camping.
For the final stretch of the route you return to C-500 and then continue south on C-536, shifting onto the D-116 at Punta de Choros, to finally return to the Inter-American Hwy about 65 km later. There are a lot of open spaces throughout this route so you’re likely to find plenty of opportunities to wild camp along the beach, which is what we did, rather than worry about finding a hotel.