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The Santa Ana River is the largest river entirely within Southern California in the United States. Its drainage basin spans four counties. It rises in the San Bernardino Mountains and flows past the cities of San Bernardino and Riverside, before cutting through the northern tip of the Santa Ana Mountains and flowing southwest past Santa Ana to drain into the Pacific Ocean. The Santa Ana River is long,〔U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. (The National Map ), accessed March 16, 2011〕 and drains a watershed of . For its size the Santa Ana drainage basin is quite diverse. It ranges from high peaks of inland mountains in the north and east, to the hot, dry interior and semi-desert basin, to flat coastal plains in the west. Its climates range from dry alpine to chaparral and desert, and the watershed as a whole is very arid. Relatively little water actually flows in the river or most of its tributaries. One of its largest tributaries, the San Jacinto River, rarely reaches the Santa Ana except in extremely wet years. The relative lack of vegetation also makes the river prone to flash flooding. Even so, a wide variety of animal and plant life has always been dependent on the river. People have lived on the Santa Ana River for at least 9,000 years. There were four distinct indigenous groups in the area, all of which depended heavily on the river for their livelihoods. The river was first crossed by Europeans in 1769, when it received its name from members of the Spanish Portola expedition. Because it is one of the largest water sources in the four-county region, many large ranchos developed alongside the river and one of its major tributaries, Santiago Creek. This period of growth culminated in the establishment of many large cities on the river, including Santa Ana, Riverside and Anaheim, all of which derived their names from the River. In the early 20th century, devastating floods poured down the Santa Ana River, leading to much of the river being channelized and dammed in recent times. ==Course== The Santa Ana River rises in Santa Ana Canyon in the southern San Bernardino Mountains, at the confluence of two tiny streams, Heart Bar Creek and Coon Creek, at an elevation of . Its highest sources are Dollar Lake, at , and Dry Lake, at , both on the northern flank of San Gorgonio Mountain, at the headwaters of a small left tributary, the South Fork Santa Ana River.〔''101 Hikes in Southern California'', p. 110〕 The river initially flows west through this broad and deep gorge, and about from its headwaters, receives its first major tributary from the right: Bear Creek, flowing southwest from well-known Big Bear Lake.〔''From Crest to Coast'', p. 10〕 The river turns south, passing through the Seven Oaks Dam, flowing out of its canyon into the arid interior basin of San Bernardino County and Riverside County, and receives Mill Creek from the left as it winds westwards towards the city of San Bernardino. As it passes through the urban area, it receives City Creek from the right and enters a flood control channel flanked by earthen levees on both sides. Not long after the confluence with City Creek, Lytle Creek enters from the right. Lytle Creek is one of the largest tributaries of the Santa Ana river, rising in three forks in the San Gabriel Mountains and flowing southeast, becoming the Lytle Creek Wash before discharging into the main stem. From there, the Santa Ana flows southwest, and after passing through the city of Riverside, it discharges into the normally dry flood control reservoir formed by Prado Dam. Two major tributaries of the river join in the reservoir area: Chino Creek from the right, and Temescal Creek from the left. Temescal Creek drains the largest area of all the tributaries, because it provides the outflow from Lake Elsinore, into which the San Jacinto River flows. It is also one of the longest, at in length. Except during the wettest years, Temescal Creek contains little or no water because Lake Elsinore is not high enough to overflow.〔〔''From Crest to Coast'', p. 11〕 After flowing out of the Prado Dam, the Santa Ana River cuts a second Santa Ana Canyon, a water gap, between the northern Santa Ana Mountains and the Puente Hills and Chino Hills, crossing into Orange County. The river roughly bisects the county as it flows southwest towards the ocean. The river is then entirely diverted into spreading grounds for groundwater recharge of the aquifer of north Orange County, providing about half of the entire county's municipal water. Downstream of there, the river serves only for flood control and waste drainage purposes, and typically has no more than a trickle of water. Passing the cities of Orange and Anaheim, it receives Santiago Creek from the east as it enters the city of Santa Ana. Here, the river is entirely confined to a concrete flood control channel between earthen levees. After crossing under Interstate 5 the riverbed again becomes earthen for a time and then becomes concrete again through most of Santa Ana and past the 405 Freeway. It flows to its mouth between Huntington Beach and Costa Mesa. The river accretes in a small lagoon before flowing out to sea at the northern end of Santa Ana River County Beach.〔〔''From Crest to Coast'', p. 12〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Santa Ana River」の詳細全文を読む スポンサード リンク
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