Islay Hill, Mountain summit in San Luis Obispo County, California, US.

Islay Hill is a mountain summit in San Luis Obispo County, California, forming part of the Nine Sisters range. The hike climbs through open grassland dotted with oak trees to reach the peak.

Islay Hill is a volcanic neck, or plug, roughly 20 million years old, formed when the region was still volcanically active. It is the southernmost of the Nine Sisters, a chain of extinct and possibly dormant volcanic plugs running from Morro Bay southeast to the hill on the southeast side of San Luis Obispo. The other eight peaks in the chain are also volcanic plugs.

Islay Hill is the southernmost of the Nine Sisters, a chain of extinct but possibly dormant volcanic plugs running from Morro Bay southeast to the hill on the southeast side of San Luis Obispo. The name links the hill to the other eight peaks of the chain, which visitors can trace across the landscape.

The trailhead at Sweet Bay Lane offers free parking and well-maintained dirt paths that need no permits. The climb is steady and manageable for visitors of varied hiking experience.

A wooden marker stands at the summit to help visitors identify the Santa Lucia Mountains and Edna Valley vineyards across the landscape. This reference point guides sightlines toward distant geographical features.