St. Joseph Catholic Church might be Yreka's oldest church. The following text is taken from the church's website regarding its history:
The Beginnings
The Catholic church in Siskiyou County most likely had its beginnings in the summer of 1853. Father James Croke, working on the Oregon mission, was traveling on horseback through the section around Jacksonville, and tradition has it that he came down as far as Yreka to hold services for the miners there, as well as in the camps of the surrounding diggings.
In the fall of 1854, Father Hugh Gallagher had returned from his trip to Europe, and with him came two young Irish priests destined for the missions in California. They were Father James Cassin and Father Thomas Cody, from the Diocese of Dublin, Ireland. On July 18, 1855, these two young Irish priests were appointed to serve as pastor and assistant by Bishop O'Connell of the San Francisco Diocese to serve Yreka in the Siskiyou District, with jurisdiction also over Crescent City in Del Norte County on the coast.
Church services were held temporarily in a little building on Yama Street, while a larger church was being built by Father Cassin on a little elevation just west of the Catholic Cemetery on the east side of town. The frame church on Cemetery Hill, completed in the fall of 1855, was considered the first Roman Catholic Church building in Yreka.
This 1855 church was obviously too close to the Yreka Creek, which had a habit of flooding, and plans were made for another structure, one safer and more convenient. This next church, a brick structure, was erected on the southeast corner of Fourth and Lane Streets. Its formal dedication was held on May 3, 1867. On the Fourth of July, 1871, fire broke out in a Chinese laundry on Miner Street, creating a raging, three-day fire; it engulfed and destroyed both the church and parish house.
Fortunately,in February of 1871 the Sisters of Mercy had arrived from New Hampshire and Mass for the parishioners could be said in their convent. By 1872 St. Joseph's Academy for Young Ladies was operating. The opening of the Academy, however, coincided with a downturn in Yreka's economic fortunes: mines were worked out, and people were moving away. The Sisters remained until January 1882 when they moved from Yreka, some going to Rio Vista and others to Red Bluff. From 1960 to 1971 Sisters of the Holy Family provided religious education classes for the youth line the parish.
Current Church
It took four years before arrangements for a new church edifice were complete. Construction of the present St. Joseph's Church was begun in 1875, taking more than one year to complete. The cornerstone was laid in September, 1876, and on Christmas Eve, 1876, Midnight Mass inaugurated services in the new church. Eventually the parish served three missions: Hawkinsville, Hilt, and Hornbrook.
A parish house built on the south end of the lot in 1887 served as rectory until 1938, when the present rectory was built. The parish hall (north of the church) was built in 1950-51. In September of 1955 an addition to the church was built. Services were held in the parish house during construction. The newly enlarged church was opened for Mass on June 10, 1956. This is the church that continues to serve the Catholic Community in the Yreka area today.
In 1976 parishioners celebrated the Centennial of St. Joseph's Church. From 2002-2004 Sr. Anne Chester served as parish steward while Fort Jones priest, Father John Lawrence, took care of the sacramental services. During the pastorate of Father Maurice O'Brien (2004-2007), the parishioners celebrated the Sesquicentennial of St. Joseph Church. On August 7, 2007, Bishop William K. Weigand officiated a Mass of Thanksgiving for 150 years of Eucharistic celebration. In July 2007 Father Bernard Tape became the pastor with his parochial vicar Father Felipe Paraguaya who was succeeded in 2009 by Father Aldrin Basarte.
There is also another historical blog site that details this church's history here. In addition, at the front entrance to the church hang two plaques that commemorate the church's centennial year (1876-1976) as well as its centennial mass that was held September 30, 1976.