When her husband George disappears after a flight into northern British Columbia's interior wilderness to search for gold, Andrea Spalding (Kim Basinger) contacts Jean Dupre (Nick Mancuso) for help, who just happens to be available for hire after intimidating a surly passenger with aerobatics in a Molyco Company Cessna 206, then landing and walking away from the aircraft as it continues to taxi onto an active runway into the path of a landing Cessna 185, with the Molyco executive still on board.
Together, Dupre and Spalding embark on a search in a dilapidated de Havilland Canada DHC-2 Beaver. Along the way, they recover from a mechanical breakdown and encounter native fisherman Elijah (John Marley), who earnestly urges them to stay away from "Headwater".
On arrival at Headwater, Dupre accidentally crashes the aircraft during the water landing, yet he and Spalding survive, shaken but unhurt. From there, the pair become involved in suspicious activities with Silas McGee (Charlton Heston), a prospector and hermit intent on protecting his silver mine. Encountering his brother, Ian McGee (Charlton Heston), their search turns into a whodunit mystery/adventure, involving mistaken identities, greed and murder. When Dupre discovers the Mollyco aircraft in which George Spalding was last seen, submerged in a lake, the searchers eventually learn the truth about Spalding's disappearance.
Mother Lode involved members of Charlton Heston's family. While he directed and starred, his son Fraser Clarke Heston came up with the idea, wrote the script and acted as producer, while his wife Lydia is credited as still photographer. "The family firm, Agamemnon Films, produced the film, and along with several other long-lost titles it's been licensed for distribution through Warner Home Video." The featurette that accompanied the DVD release revealed: "... Fraser Heston admits to being heavily influenced by John Huston's masterpiece 'The Treasure of the Sierra Madre' (1948) though structurally the film is like a Canuck version of Peter Benchley's The Deep: young adventurer becomes obsessed with buried treasure; voluptuous girlfriend wants to pack up and go home; eccentric but experienced treasure hunter manipulates them both."
Filming for Mother Lode took place primarily at Lake Lovely Water near Squamish, British Columbia, with most aerial scenes filmed along the Fraser River Valley. Additional photography took place near Vancouver, British Columbia.
The de Havilland Canada DHC-2 Beaver floatplane used in Mother Lode was not intended to be crashed, nor was a crash part of the original storyline. Trying a "glassy water landing", the pilot reduced his descent too late as the left float contacted, created drag and hooked, followed by the right float doing the same, whereupon all control was lost and the aircraft slewed around, flipped over, and sank. With no fiscal options remaining, the Hestons were forced to incorporate the crash into the plot. The scene is regarded by many fans as the highlight of the film.
The Beaver floatplane was recovered from the lake and transported to Kelowna, British Columbia, where it was fully restored, put back on wheels and sold to an American business, which licensed the aircraft as N323RS.
The aircraft which is landing when the Mollyco Cessna 206 wanders onto its runway is a Cessna 185, which performs an abrupt "firewall" (application of full power) and pull-up to clear the 206. Neither the Cessna 206 nor 185 was normally rated for such aerial maneuvers as depicted in the film.
Mother Lode was not well received by critics. The review in TV Guide dismissed the film as "mediocre".
Variety was more positive: "As the title indicates, the consuming issue in Mother Lode is a search for gold. The picture is not without shortcomings, but is long on good performances, charismatic people in the three principal roles, compelling outdoor aerial sequences in the Cassiar Mountains of British Columbia and high-level suspense throughout."
Mother Lode had a very limited cinematic release in the United States, and a limited VHS release shortly after, with a DVD release on March 29, 2011. The film has yet to be released in Blu-ray format. In a review of the DVD version, Stuart Galbraith IV of DVD Talk thought the film worked best as a thriller and was "occasionally extremely effective".