From the First Great Western Website :

‘RideCornwall’ is a one-day Rover retailed by railway booking offices, train managers/conductors and bus drivers. The ‘RideCornwall’ product gives the holder one day’s unlimited travel on all rail and most bus services within Cornwall and between Cornwall and Plymouth, after 09:00 Monday – Friday and at any time on Saturdays, Sundays and Bank Holidays.

‘Ride Cornwall’ is valid on the following operator’s services:

Rail

First Great Western
Virgin Trains

Bus (only within Cornwall or to/from the City of Plymouth on routes from/to Cornwall)

First Devon & Cornwall
Western Greyhound
Truronian

Prices

‘RideCornwall’ is available for one day:

Adult - £12.00
Child - £7.50
Family (up to 2 adults and 3 children) - £24.00

Restrictions

‘RideCornwall’ is not valid for use on any rail or bus service before 09:00 Monday – Friday

‘RideCornwall’ may be used at any time on Saturdays, Sundays or Bank Holidays

‘RideCornwall’ is valid for use on all rail services in Cornwall and also between Cornwall and Plymouth and on the Gunnislake ‘Tamar Valley’ branch line.

‘RideCornwall’ is valid for use on the bus operators listed for all journeys within Cornwall and also for journeys between Cornwall and Plymouth.

‘RideCornwall’ is not valid for local bus journeys within the City of Plymouth or on the services of bus operators not listed, including Plymouth CityBus.