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Abstract. Salmon redds and carcasses were surveyed on the mainstem Trinity River, from Lewiston Dam to the confluence with the Klamath River, during the 2012–2014 spawning seasons to map spawning distribution, evaluate pre-spawn mortality, and characterize redds by species and spawner origin. We applied generalized additive models to the spatiotemporal distribution of unmarked and hatchery-marked spawned female salmon carcasses to apportion redd counts by natural- and hatchery-origin Chinook Salmon Oncorhynchus tshawytscha. The annual estimated numbers of redds constructed by natural-origin Chinook Salmon females were 6,170, 2,682, and 2,733 from 2012 to 2014, respectively. The number of redds constructed by hatchery-origin Chinook Salmon were 1,145, 603, and 909 for the same respective time period. The distribution of redds constructed by hatchery-origin Chinook and Coho salmon were highly skewed toward Lewiston Dam. Since this project began in 2002, the number of redds constructed per year by natural-origin Chinook Salmon has been highly variable with no significant trend, while the number of redds built by hatchery-origin Chinook Salmon has trended downward. We observed an increase in the mean distance from Lewiston Dam of natural-origin Chinook Salmon redds. Between 2002 and 2014, from upstream to downstream, the number of natural-origin Chinook Salmon redds decreased in the Lewiston reach, remained unchanged in the Limekiln, Douglas City, Junction City, and North Fork reaches, increased in the Big Flat and Del Loma reaches, and remained unchanged in the South Fork, Willow Creek, and Hoopa reaches. Within channel restoration sites, spawning distribution responded to physical alterations at the local scale, but the number of redds exhibited inconsistent responses to channel rehabilitation work. Also calculated from carcass data, annual pre-spawn mortality in the survey area ranged between 2.4% and 11.5% from 2009 to 2014.