Question: What did the Spokane and Inland Empire Railroad merge into that operated between 1970 and 1996?

Context paragraphs:
Washington State Route 27: State Route 27 (SR 27) is a 90 mi state highway serving Whitman and Spokane counties, located in the eastern region of the U.S. state of Washington.  The highway travels generally north from U.S. Route 195 (US 195) through Pullman, Palouse, Tekoa, and Spokane Valley to SR 290 north of an interchange with Interstate 90 (I-90).  SR 27 serves the Palouse region as part of the Palouse Scenic Byway and travels between US 195 to the west and US 95 to the east in Idaho, with several auxiliary routes connecting to the two other highways.  The highway has been part of the state highway system since 1913, as a part of the Second Division of the Eastern Route of the Inland Empire Highway between Pullman and Oakesdale that later became a branch of Primary State Highway 3 (PSH 3), as well as Secondary State Highway 3H (SSH 3H) in 1937.  Both highways were combined to form SR 27 during the 1964 highway renumbering and the designation was extended south to the US 195 bypass of Pullman in 1975 and north to SR 290 in 1991.

Frequency Changing Station: The Frequency Changing Station in Spokane, Washington is a building listed on the National Register of Historic Places.  It was built by the Spokane and Inland Empire Railroad in 1908 to house electrical equipment used by the electric railway.  Power was generated at the Nine Mile Falls dam and transmitted to the Frequency Changing Station.  The station provided direct current to the streetcar network within the city of Spokane.  To provide power to the rail network outside Spokane, the station converted a portion of the power to alternating current and fed it to a series of electrical substations spaced about 15 mi on the operating line.  The substations then converted power back to direct current for the streetcars, but also sold power at 110 volts AC to the communities.

Cowles Company: The Cowles Company is a diversified media company in Spokane, Washington in the US.  The company owns and operates the newspaper "The Spokesman-Review" in Spokane, founded in 1894.  The company operates Inland Empire Paper Company, television stations, and interests in real estate, insurance, marketing and financial services.

Old National Bank Building: The Old National Bank building, located in Spokane, Washington, was completed in 1911 and was the first skyscraper located in the Inland Northwest.  This fifteen story tower reaches to a height of 217 feet (66 m) above the Spokane valley and remained the tallest building in the city until the Paulsen Center was completed across the street on Riverside Ave. The Old National Bank building served as a symbol of prosperity for the rising economy of the Inland Empire.

Spokane and Inland Empire Railroad: The Spokane and Inland Empire Railroad Company (S.&I.E.R.R.Co.)  was an electrified interurban railway operating in Spokane, Washington and vicinity, extending into northern and central Idaho.  The system originated in several predecessor roads beginning c. 1890, incorporated in 1904, and ran under its own name to 1929.  It merged into the Great Northern Railway and later, the Burlington Northern Railroad, which operated some roads into the 1980s.

Burlington Northern Railroad: The Burlington Northern Railroad (reporting mark BN) was a United States-based railroad company formed from a merger of four major U.S. railroads.  Burlington Northern operated between 1970 and 1996.

Inland Empire Blues Society: The Inland Empire Blues Society (IEBS) is a nonprofit organization dedicated to supporting, preserving and promoting the blues through social events, such as concerts, festivals, and a newsletter.  IEBS is a member of the Blues Foundation.  Although based in Spokane Washington, IEBS represents a broader area generally known as the Inland Empire of the Pacific Northwest.

Playfair Race Course: Playfair Race Course, (known as the Spokane Interstate Fair from 1901–1935) was the home of horse racing in Spokane, Washington, from 1901 to 2000.  The track started out as a four furlong oval, later expanded to five furlongs in 1946.  The premier races run at the track were the Playfair Mile, Spokane Derby, and Inland Empire Marathon.

San Bernardino, California: San Bernardino is a city located in the Riverside-San Bernardino metropolitan area (sometimes called the "Inland Empire").  It serves as the county seat of San Bernardino County, California, United States.  As one of the Inland Empire's anchor cities, San Bernardino spans 81 sqmi on the floor of the San Bernardino Valley and has a population of 209,924 as of the 2010 census.  San Bernardino is the 17th-largest city in California and the 100th-largest city in the United States.  San Bernardino is home to numerous diplomatic missions for the Inland Empire, being one of four cities in California with numerous consulates (the other three being Los Angeles, San Diego and San Francisco).  The governments of Guatemala and Mexico have also established their consulates in the downtown area of the city.

Nine Mile Dam: Nine Mile Falls Dam is a dam on the Spokane River, in the unincorporated community of Nine Mile Falls, Washington.  It was built on the site of the falls in 1908, creating Nine Mile Reservoir.  The dam was designed by the New York engineering firm of Sanderson & Porter, and originally constructed to satisfy the power needs of the Spokane and Inland Empire Railroad interurban trolley lines.

Supporting paragraphs: Spokane and Inland Empire Railroad Burlington Northern Railroad
Answer: Burlington Northern Railroad