also see: Risk management principles for trails and outdoor recreation

Sovereign immunity for trail conditions (some limitations for situations where the governmental agency creates the trail):

Government Code

(source)

• TITLE 1. GENERAL [100. – 7914.] ( Title 1 enacted by Stats. 1943, Ch. 134. )

  • DIVISION 3.6. CLAIMS AND ACTIONS AGAINST PUBLIC ENTITIES AND PUBLIC EMPLOYEES [810. – 998.3.] ( Division 3.6 added by Stats. 1963, Ch. 1681. )

    • PART 2. LIABILITY OF PUBLIC ENTITIES AND PUBLIC EMPLOYEES [814. – 895.8.] ( Part 2 added by Stats. 1963, Ch. 1681. )

      • CHAPTER 2. Dangerous Conditions of Public Property [830. – 840.6.] ( Chapter 2 added by Stats. 1963, Ch. 1681. )

        •  ARTICLE 1. General [830. – 831.8.] ( Article 1 added by Stats. 1963, Ch. 1681. )

831.4. A public entity, public employee, or a grantor of a public
easement to a public entity for any of the following purposes, is not
liable for an injury caused by a condition of:

(a) Any unpaved road which provides access to fishing, hunting,
camping, hiking, riding, including animal and all types of vehicular
riding, water sports, recreational or scenic areas and which is not a

(1) city street or highway or (2) county, state or federal highway
or (3) public street or highway of a joint highway district,
boulevard district, bridge and highway district or similar district
formed for the improvement or building of public streets or highways.

(b) Any trail used for the above purposes.

(c) …

831.7. (a) Neither a public entity nor a public employee is liable
to any person who participates in a hazardous recreational activity,
including any person who assists the participant, or to any spectator
who knew or reasonably should have known that the hazardous
recreational activity created a substantial risk of injury to himself
or herself and was voluntarily in the place of risk, or having the
ability to do so failed to leave, for any damage or injury to
property or persons arising out of that hazardous recreational
activity.

(b) As used in this section, “hazardous recreational activity”
means a recreational activity conducted on property of a public
entity that creates a substantial, as distinguished from a minor,
trivial, or insignificant, risk of injury to a participant or a
spectator.

“Hazardous recreational activity” also means:
(1) …
(2) …
(3) Animal riding, including equestrian competition, archery,
bicycle racing or jumping, mountain bicycling, boating, cross-country
and downhill skiing, hang gliding, kayaking, motorized vehicle
racing, off-road motorcycling or four-wheel driving of any kind,
orienteering, pistol and rifle shooting, rock climbing, rocketeering,
rodeo, self-contained underwater breathing apparatus (SCUBA) diving,
spelunking, skydiving, sport parachuting, paragliding, body contact
sports, surfing, trampolining, tree climbing, tree rope swinging,
waterskiing, white water rafting, and windsurfing. For the purposes
of this subdivision, “mountain bicycling” does not include riding a
bicycle on paved pathways, roadways, or sidewalks..

(c) (1) Notwithstanding subdivision (a), this section does not
limit liability that would otherwise exist for any of the following:

(A) Failure of the public entity or employee to guard or warn of a
known dangerous condition or of another hazardous recreational
activity known to the public entity or employee that is not
reasonably assumed by the participant as inherently a part of the
hazardous recreational activity out of which the damage or injury
arose.

(B) Damage or injury suffered in any case where permission to
participate in the hazardous recreational activity was granted for a
specific fee. For the purpose of this subparagraph, “specific fee”
does not include a fee or consideration charged for a general purpose
such as a general park admission charge, a vehicle entry or parking
fee, or an administrative or group use application or permit fee, as
distinguished from a specific fee charged for participation in the
specific hazardous recreational activity out of which the damage or
injury arose.

(C) Injury suffered to the extent proximately caused by the
negligent failure of the public entity or public employee to properly
construct or maintain in good repair any structure, recreational
equipment or machinery, or substantial work of improvement utilized
in the hazardous recreational activity out of which the damage or
injury arose.

(D) Damage or injury suffered in any case where the public entity
or employee recklessly or with gross negligence promoted the
participation in or observance of a hazardous recreational activity.
For purposes of this subparagraph, promotional literature or a public
announcement or advertisement that merely describes the available
facilities and services on the property does not in itself constitute
a reckless or grossly negligent promotion.

(E) An act of gross negligence by a public entity or a public
employee that is the proximate cause of the injury.

(2) Nothing in this subdivision creates a duty of care or basis of
liability for personal injury or damage to personal property.

(d) Nothing in this section limits the liability of an independent
concessionaire, or any person or organization other than the public
entity, whether or not the person or organization has a contractual
relationship with the public entity to use the public property, for
injuries or damages suffered in any case as a result of the operation
of a hazardous recreational activity on public property by the
concessionaire, person, or organization.

—

The statute posted above doesn’t “cover” private landowners. Private Landowners of open lands find safe haven in California Civil Code 846:

846. An owner of any estate or any other interest in real property,
whether possessory or nonpossessory, owes no duty of care to keep
the premises safe for entry or use by others for any recreational
purpose or to give any warning of hazardous conditions, uses of,
structures, or activities on such premises to persons entering for
such purpose, except as provided in this section.
A “recreational purpose,” as used in this section, includes such
activities as fishing, hunting, camping, water sports, hiking,
spelunking, sport parachuting, riding, including animal riding,
snowmobiling, and all other types of vehicular riding, rock
collecting, sightseeing, picnicking, nature study, nature contacting,
recreational gardening, gleaning, hang gliding, winter sports, and
viewing or enjoying historical, archaeological, scenic, natural, or
scientific sites.
An owner of any estate or any other interest in real property,
whether possessory or nonpossessory, who gives permission to another
for entry or use for the above purpose upon the premises does not
thereby (a) extend any assurance that the premises are safe for such
purpose, or (b) constitute the person to whom permission has been
granted the legal status of an invitee or licensee to whom a duty of
care is owed, or (c) assume responsibility for or incur liability for
any injury to person or property caused by any act of such person to
whom permission has been granted except as provided in this section.
This section does not limit the liability which otherwise exists
(a) for willful or malicious failure to guard or warn against a
dangerous condition, use, structure or activity; or (b) for injury
suffered in any case where permission to enter for the above purpose
was granted for a consideration other than the consideration, if any,
paid to said landowner by the state, or where consideration has been
received from others for the same purpose; or (c) to any persons who
are expressly invited rather than merely permitted to come upon the
premises by the landowner.
Nothing in this section creates a duty of care or ground of
liability for injury to person or property.