On the face of it, this appears to be due to landslide triggered by a violent storm; in legal terms, an "Act of God" for which no one is responsible.
There are individuals/corperations/entities who could be partially responsible; however, it is important to note that Highway 1 is old. Its construction began in 1934. Roads don't last forever, especially seaside roads.
Potentially responsible people include:
- Road builders, if shoddy or substandard construction contributed to the collapse.
- Engineers, if road was of unsound design which contributed to the collapse (note that the seaside location was almost certainly a design requirement that was worked around).
- Road Maintainers (currently CalTrans, the state transportation department): If poor or inadequate maintenance lead to the collapse.
However, there is at the current moment no evidence that suggest any of the above failed in their duties.